Deleting snapshot may take time. The current volume API does not allow
to delete volumes with snapshots, so if deleting snapshot may take time,
a delete request for a parent volume will fail.
This sometimes causes functional test failures in slow environments.
wait_for_status() checks whether volume status is in error statuses
but previously the expected error status was wrong. Cinder API uses
lower case as volume status, so it did not work expectedly.
Change-Id: I095894ba39f23bf81d71351818d24dbb5ca459fb
eeb614c477