Add status check for creating volume backup

When creating volume backup from volume or snapshot, the status of the
source volume or snapshot will be changed to 'backing-up', and will be
changed to volume or snapshot's original status after the backup
creation finished. So it is necessary to add status check for the source
volume or snapshot to make the tests more robust.

Change-Id: I0add3989e1184012b908c5fab459cda41194dec3
4 files changed