region-config settings for cloud ignored

juju bootstrap is not picking up region-config config from the cloud config settings.

$ juju version
2.3-alpha1-yakkety-amd64 (built from develop on Jun 22)
$ juju show-cloud serverstack-os
defined: local
type: openstack
description: Openstack Cloud
auth-types: [userpass]
endpoint: http://<ip addr>:5000/v3
regions:
  serverstack: {}
region-config:
  serverstack:
    network: admin_net
    use-floating-ip: true
$ juju bootstrap --metadata-source ./simplestreams serverstack-os/serverstack
Creating Juju controller "serverstack-os-serverstack" on serverstack-os/serverstack
Looking for packaged Juju agent version 2.3-alpha1 for amd64
No packaged binary found, preparing local Juju agent binary
Launching controller instance(s) on serverstack-os/serverstack...
ERROR failed to bootstrap model: cannot start bootstrap instance: cannot run instance: failed to run a server with nova.RunServerOpts{Name:"juju-d6476e-controller-0", FlavorId:"3", ImageId:"1eded0b1-476f-40ea-9257-f0e207efecdc", UserData:[]uint8{0x1f, 0x8b, 0x8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xff, 0x9c, 0x96, 0xe9, 0xce, 0xab, 0xca, 0x72, 0xf7, 0xbf, 0x3f, 0x57, 0x81, 0xf4, ...
 0x8e, 0x8d, 0xf, 0x0, 0x0}, SecurityGroupNames:[]nova.SecurityGroupName{nova.SecurityGroupName{Name:"juju-466f3577-4c90-483e-8b07-169525577b20-d0d4fba7-7f78-499f-86f6-f3b699d6476e"}, nova.SecurityGroupName{Name:"juju-466f3577-4c90-483e-8b07-169525577b20-d0d4fba7-7f78-499f-86f6-f3b699d6476e-0"}}, Networks:[]nova.ServerNetworks{}, AvailabilityZone:"nova", Metadata:map[string]string{"juju-model-uuid":"d0d4fba7-7f78-499f-86f6-f3b699d6476e", "juju-controller-uuid":"466f3577-4c90-483e-8b07-169525577b20", "juju-is-controller":"true"}, ConfigDrive:false}
caused by: request (http://<ip addr>:8774/v2.1/010ab46135ba414882641f663ec917b6/servers) returned unexpected status: 409; error info: {"conflictingRequest": {"message": "Multiple possible networks found, use a Network ID to be more specific.", "code": 409}}

$ juju bootstrap --metadata-source ./simplestreams serverstack-os
same result as above

Updated the cloud config:

$ juju show-cloud serverstack-os
defined: local
type: openstack
description: Openstack Cloud
auth-types: [userpass]
endpoint: http://<ip addr>:5000/v3
regions:
  serverstack: {}
config:
  network: admin_net
region-config:
  serverstack:
    network: admin_net
    use-floating-ip: true
$ juju bootstrap --metadata-source ./simplestreams serverstack-os
Creating Juju controller "serverstack-os-serverstack" on serverstack-os/serverstack
Looking for packaged Juju agent version 2.3-alpha1 for amd64
No packaged binary found, preparing local Juju agent binary
Launching controller instance(s) on serverstack-os/serverstack...
 - 37bfecc7-a09e-4205-8b3c-99828f23123b (arch=amd64 mem=4G cores=2), wait 10 seconds before retry, attempt 2
Fetching Juju GUI 2.7.3
...