Dell SC: Add support for driver retype

Dell SC: Add support for driver retype

Previously there was no need to support retype by the driver
since any kind of retyping would require migration. With the
addition of the ability to set specific Storage Profiles to
use by commit Icf76fceca5a0ae20bb08b276b0c41ef6cdb31087 we
now have something the driver can handle to optimize the
retyping operation.

This adds handling for changes in the selected Storage Profile
if the backend stays the same. Any other retype changes will
return failure, resulting in it falling back to full volume
migration.

Change-Id: I18c55e0392e18d1686546ba17cb99b53b7b50566