VolumeMultiBackendTest: delete error volumes

Record the volume ID before waiting for the volume status to go
available. This means that if the volume goes into error the tearDown
method can remove the volume.

Change-Id: I67e74af999862fc37c4f5b2474b50b62cce328e9
Partial-Bug: #1352498
Merge "VolumeMultiBackendTest: delete error volumes"