Cleans up volume backups after test run.

1. Updated class level create_backup function to wait for resource delete
2. Added start_time, end_time, wait_time to the timeout exception message
   to verify the test case waits for the build_timeout before throwing
   the timeout exception
3. Updated the test case

https: //storyboard.openstack.org/#!/story/2008683
Change-Id: I4819b88c6789544124b67ab67b07141f1c50f36b
3 files changed