Add optimized volume migration to Storwize/SVC

Add an optimized migration path for when the source and destination are
managed by the same storage. If the source and destination pools have
the same extent_size, it will use the optimal migratevdisk command.
Otherwise, it will use addvdiskcopy and rmvdiskcopy, which must be
watched until the copies are sync'ed.

Change-Id: Ic6069422f5ac7f963f4b1268c0d632a038a8474f
Merge "Add optimized volume migration to Storwize/SVC"