GlusterFS: Delete volume-<uuid>.info file when volume is deleted.

glusterfs creates a file named volume-<uuid>.info to hold volume
data, mapping cinder snapshot UUIDs and filenames. When the
volume and its associated snapshots are both deleted, this file
remains. This patch deletes the volume-<uuid>.info (if one exists)
when the volume is deleted.

Change-Id: Iefc8bd4768b30a75c648c4689d935daeab3afe98
Closes-Bug: #1299182
(cherry picked from commit bf006ecb4a52db6300aa0fe1abe7df621e9f6174)
GlusterFS: Delete active snapshot file on volume delete.

If a snapshot is taken of a volume that is attached to an active
instance, the volume file used by the instance will be switched to
the new snapshot file that is created.  When you delete the
snapshot, the base volume file will be merged with the snapshot
file and the base volume is deleted.  Upon a deleting the active
volume, the active snapshot file is not deleted because it does not
have the expected name that cinder is looking for, i.e.
volume-<uuid>.  Instead, the snapshot file has the name
volume-<uuid>.<snapshot-uuid>.  This patch looks at the volume info
file to find any active snapshot file and properly delete it when
the volume is deleted.

Change-Id: Ib0af4401d839ec3bd1eb3a81e1671811e0d4a288
Closes-Bug: #1300303
(cherry picked from commit 5f00cad02da1093d71f636add0810a538cbd444f)