Remove race due to 1907084

The test_attach_scsi_disk_with_config_drive test cases is racy at volume
detach. Nova first detach the volume in cinder then later deletes the
BlockDeviceMapping from the nova DB. Test waits for the volume to become
available and then checks the list of volume attachments in the nova API
then it can see that the attachment is still there.

Closes-Bug: #1907084
Change-Id: I814ae3215f39d1e8407c4ca1c7117a314941c80b
3 files changed