The patch provided fixed the issue for me when doing virtio-scsi boot from RBD volume + config drive on Ocata.

However, I do see a lingering issue on an instance which has 2 virtio-scsi RBD volumes attached. One volume is the boot device and is marked bootable in Cinder. The other volume is a storage disk and is not marked bootable in cinder. Nova keeps generating the libvirt XML with the storage disk listed as LUN 0, and the boot disk listed as LUN 1, breaking the instance boot. Viewing the volume in Cinder shows the correct boot device listed as mounted at /dev/sda.

For reference below:
Boot volume: a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a
Data volume: e82a7785-1c8c-4931-8948-4e16838f840e

ubuntu@7b25e53036d7:~$ openstack volume show e82a7785-1c8c-4931-8948-4e16838f840e
+--------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Field                          | Value                                                                                                                                                                                                                                                                                                                  |
+--------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| attachments                    | [{u'server_id': u'd83da61f-de88-4180-a434-71a64db3182e', u'attachment_id': u'c5f956ea-0c2d-43a2-8151-d481124b5a6e', u'attached_at': u'2017-11-20T12:07:22.000000', u'host_name': None, u'volume_id': u'e82a7785-1c8c-4931-8948-4e16838f840e', u'device': u'/dev/sdb', u'id': u'e82a7785-1c8c-4931-8948-4e16838f840e'}] |
| availability_zone              | us-dfw-1                                                                                                                                                                                                                                                                                                               |
| bootable                       | false                                                                                                                                                                                                                                                                                                                  |
| consistencygroup_id            | None                                                                                                                                                                                                                                                                                                                   |
| created_at                     | 2016-10-09T03:36:58.000000                                                                                                                                                                                                                                                                                             |
| description                    |                                                                                                                                                                                                                                                                                                                        |
| encrypted                      | False                                                                                                                                                                                                                                                                                                                  |
| id                             | e82a7785-1c8c-4931-8948-4e16838f840e                                                                                                                                                                                                                                                                                   |
| migration_status               | None                                                                                                                                                                                                                                                                                                                   |
| multiattach                    | False                                                                                                                                                                                                                                                                                                                  |
| name                           | miscstore                                                                                                                                                                                                                                                                                                              |
| os-vol-host-attr:host          | ceph-us-dfw-1@HDD#rbddriver-hdd                                                                                                                                                                                                                                                                                        |
| os-vol-mig-status-attr:migstat | None                                                                                                                                                                                                                                                                                                                   |
| os-vol-mig-status-attr:name_id | None                                                                                                                                                                                                                                                                                                                   |
| os-vol-tenant-attr:tenant_id   | 4450a82f9deb45668f35ce712fc74074                                                                                                                                                                                                                                                                                       |
| properties                     | attached_mode='rw', readonly='False'                                                                                                                                                                                                                                                                                   |
| replication_status             | disabled                                                                                                                                                                                                                                                                                                               |
| size                           | 1500                                                                                                                                                                                                                                                                                                                   |
| snapshot_id                    | None                                                                                                                                                                                                                                                                                                                   |
| source_volid                   | None                                                                                                                                                                                                                                                                                                                   |
| status                         | in-use                                                                                                                                                                                                                                                                                                                 |
| type                           | HDD                                                                                                                                                                                                                                                                                                                    |
| updated_at                     | 2017-11-20T12:07:22.000000                                                                                                                                                                                                                                                                                             |
| user_id                        | 5efbfc26106b4a6badb457c34e745a11                                                                                                                                                                                                                                                                                       |
+--------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
ubuntu@7b25e53036d7:~$ openstack volume show a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a
+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Field                          | Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| attachments                    | [{u'server_id': u'd83da61f-de88-4180-a434-71a64db3182e', u'attachment_id': u'202e1703-16dd-419a-ab68-091ad98470f9', u'attached_at': u'2017-10-10T14:37:34.000000', u'host_name': None, u'volume_id': u'a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a', u'device': u'/dev/sda', u'id': u'a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a'}]                                                                                                                                                                                                                                                                                                                                                                                               |
| availability_zone              | us-dfw-1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| bootable                       | true                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| consistencygroup_id            | None                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| created_at                     | 2016-09-20T23:41:33.000000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| description                    |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| encrypted                      | False                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| id                             | a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| migration_status               | None                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| multiattach                    | False                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| name                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| os-vol-host-attr:host          | ceph-us-dfw-1@HDD#rbddriver-hdd                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
| os-vol-mig-status-attr:migstat | None                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| os-vol-mig-status-attr:name_id | None                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| os-vol-tenant-attr:tenant_id   | 4450a82f9deb45668f35ce712fc74074                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| properties                     | attached_mode='rw', readonly='False'                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| replication_status             | disabled                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| size                           | 150                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| snapshot_id                    | None                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| source_volid                   | None                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
| status                         | in-use                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| type                           | HDD                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| updated_at                     | 2017-10-10T14:37:34.000000                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
| user_id                        | 5efbfc26106b4a6badb457c34e745a11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| volume_image_metadata          | {u'hw_qemu_guest_agent': u'True', u'os_distro': u'ubuntu', u'os_require_quiesce': u'True', u'container_format': u'bare', u'min_ram': u'0', u'disk_format': u'raw', u'image_name': u'Ubuntu 16.04 LTS (Xenial) 64 Bit [20160809-1]', u'owner_specified.shade.sha256': u'9700e1862392c33bda7e2beec9c1e244a4df4291c05293b6da7557280ba99a6d', u'hw_scsi_model': u'virtio-scsi', u'image_id': u'd129e4fe-c0f2-4563-9238-2cde3ac0354f', u'owner_specified.shade.object': u'images/Ubuntu 16.04 LTS (Xenial) 64 Bit [20160809-1]', u'checksum': u'0d8d582f1c420f6352f97cff6c1d3a23', u'min_disk': u'0', u'owner_specified.shade.md5': u'0d8d582f1c420f6352f97cff6c1d3a23', u'hw_disk_bus': u'scsi', u'size': u'1759510528'} |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

from dumpxml for the instance:
<disk type='network' device='disk'>
  <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
  <auth username='cinder'>
    <secret type='ceph' uuid='<snip>'/>
  </auth>
  <source protocol='rbd' name='openstack_volumes/volume-a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a'>
    <host name='<snip>' port='6789'/>
    <host name='<snip>' port='6789'/>
    <host name='<snip>' port='6789'/>
  </source>
  <backingStore/>
  <target dev='sda' bus='scsi'/>
  <serial>a63ea64e-a4fe-4bdb-98d9-a9a48e773f1a</serial>
  <alias name='scsi0-0-0-1'/>
  <address type='drive' controller='0' bus='0' target='0' unit='1'/>
</disk>
<disk type='network' device='disk'>
  <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
  <auth username='cinder'>
    <secret type='ceph' uuid='<snip>'/>
  </auth>
  <source protocol='rbd' name='openstack_volumes/volume-e82a7785-1c8c-4931-8948-4e16838f840e'>
    <host name='<snip>' port='6789'/>
    <host name='<snip>' port='6789'/>
    <host name='<snip>' port='6789'/>
  </source>
  <backingStore/>
  <target dev='sdb' bus='scsi'/>
  <serial>e82a7785-1c8c-4931-8948-4e16838f840e</serial>
  <alias name='scsi0-0-0-0'/>
  <address type='drive' controller='0' bus='0' target='0' unit='0'/>
</disk>