Unmanage and manage snapshots

This feature provides the ability to import/export volume snapshot
from one Cinder to another and to import snapshots that have not been
managed by Cinder from a storage back end to Cinder.

Added:
- Api for snapshot-unmange
- Api for snapshot-manage
- New client 'snapshot_manage_client'
- 'delete_snapshot' method
Note: Cinder V1 does not support unmanage & manage snapshot.

Change-Id: Ib02fe171b07814aa12d311171dceac834ecbfe39
7 files changed