HP LeftHand Backend assisted volume migrate

HP LeftHand Backend assisted volume migrate

This patch implements volume migrate using native LeftHand APIs.

Limitations:
1. Same LeftHand backend
2. Volume cannot be attached
3. Volumes with snapshots cannot be migrated
4. Source and Destination clusters must be in the same management group
5. Volume re-type not supported

Change-Id: I503d5a10ee59db14130c676a5c3a07abf9a2b7af
Implements: blueprint native-lefthand-volume-migrate