Only enforce multiattach policy for retype target
Only enforce multiattach policy for retype target

We should only be checking multiattach policy if the target
of a retype is multiattach capable. If they are already on
a type and policy has changed, we should not block retyping.

Change-Id: Id4cfb7771439940c59b828ea7f1d95bcfe7d1e26

j-griffith/cinder,openstack/cinder,phenoxim/cinder,mahak/cinder,openstack/cinder,phenoxim/cinder,j-griffith/cinder,mahak/cinder