DeviceTaggingTestV2_42.test_device_tagging randomly fails with "mount: mounting /dev/sr0 on /mnt failed: Device or resource busy"

http://logs.openstack.org/66/483566/10/check/gate-tempest-dsvm-neutron-nova-next-full-ubuntu-xenial-nv/c816bd9/logs/tempest.txt.gz#_2017-07-24_16_43_36_846

2017-07-24 16:43:36.846 1571 ERROR tempest.lib.common.utils.linux.remote_client [-] (DeviceTaggingTestV2_42:test_device_tagging) Initializing SSH connection to 172.24.5.4 failed. Error: Command 'set -eu -o pipefail; PATH=$PATH:/sbin; sudo mount /dev/sr0 /mnt', exit status: 255, stderr:
mount: mounting /dev/sr0 on /mnt failed: Device or resource busy

stdout:
: SSHExecCommandFailed: Command 'set -eu -o pipefail; PATH=$PATH:/sbin; sudo mount /dev/sr0 /mnt', exit status: 255, stderr:
mount: mounting /dev/sr0 on /mnt failed: Device or resource busy

stdout:

http://logs.openstack.org/66/483566/10/check/gate-tempest-dsvm-neutron-nova-next-full-ubuntu-xenial-nv/c816bd9/console.html#_2017-07-24_17_19_13_176110

2017-07-24 17:19:13.176110 | tempest.api.compute.servers.test_device_tagging.DeviceTaggingTestV2_42.test_device_tagging[id-a2e65a6c-66f1-4442-aaa8-498c31778d96,image,network,volume]
2017-07-24 17:19:13.176163 | --------------------------------------------------------------------------------------------------------------------------------------------------------
2017-07-24 17:19:13.176171 |
2017-07-24 17:19:13.176181 | Captured traceback:
2017-07-24 17:19:13.176191 | ~~~~~~~~~~~~~~~~~~~
2017-07-24 17:19:13.176205 | Traceback (most recent call last):
2017-07-24 17:19:13.176221 | File "tempest/test.py", line 103, in wrapper
2017-07-24 17:19:13.176237 | return f(self, *func_args, **func_kwargs)
2017-07-24 17:19:13.176263 | File "tempest/api/compute/servers/test_device_tagging.py", line 271, in test_device_tagging
2017-07-24 17:19:13.176284 | self.ssh_client.exec_command('sudo mount %s /mnt' % dev_name)
2017-07-24 17:19:13.176307 | File "tempest/lib/common/utils/linux/remote_client.py", line 30, in wrapper
2017-07-24 17:19:13.176323 | return function(self, *args, **kwargs)
2017-07-24 17:19:13.176346 | File "tempest/lib/common/utils/linux/remote_client.py", line 105, in exec_command
2017-07-24 17:19:13.176363 | return self.ssh_client.exec_command(cmd)
2017-07-24 17:19:13.176383 | File "tempest/lib/common/ssh.py", line 202, in exec_command
2017-07-24 17:19:13.176397 | stderr=err_data, stdout=out_data)
2017-07-24 17:19:13.176433 | tempest.lib.exceptions.SSHExecCommandFailed: Command 'set -eu -o pipefail; PATH=$PATH:/sbin; sudo mount /dev/sr0 /mnt', exit status: 255, stderr:
2017-07-24 17:19:13.176464 | mount: mounting /dev/sr0 on /mnt failed: Device or resource busy
2017-07-24 17:19:13.176470 |
2017-07-24 17:19:13.176478 | stdout:

The test dumps out some lsblk information after it fails:

2017-07-24 16:43:38.010 1571 ERROR tempest.api.compute.servers.test_device_tagging [-] Mounting /dev/sr0 on /mnt failed. Right after the failure 'lsblk' in the guest reported:
NAME FSTYPE LABEL MOUNTPOINT
vda
`-vda1 ext3 cirros-rootfs /
vdb
vdc
sr0 iso9660 config-2
: SSHExecCommandFailed: Command 'set -eu -o pipefail; PATH=$PATH:/sbin; sudo mount /dev/sr0 /mnt', exit status: 255, stderr:
mount: mounting /dev/sr0 on /mnt failed: Device or resource busy

stdout:

But in this case it doesn't really tell us much. Maybe we should retry up to 3 times to mount the config drive to read from it?