3PAR: Create volume from snapshot with larger size

Refactored the migrate_volume code to be usable by both migrate volume
and create volume from snapshot with a larger size. The common functionality
is to clone a volume as a base volume. Migrate volume specifies a different
CPG, whereas create volume from snapshot uses the same CPG.

Change-Id: I4081807294d918fc0e9c2e17bae89b6df7ee1513
Closes-Bug: #1279478
3PAR: Fix extend volume GiB to MiB

Extend volume was sending GiB instead of MiB to the 3PAR
array. This patch is now sending the growth size in MiBs
instead of GiBs.

Change-Id: Ib4903315a32e090e760883cc80c50f3698fe015f
Closes-Bug: #1284368
Merge "3PAR: Create volume from snapshot with larger size"
Merge "3PAR: Fix extend volume GiB to MiB"