The last piece of service type alias support is to handle volumev2,
volumev3, workflowv2, workflowv3 and friends.
Although it's an annoying scenario, luckily legacy code that uses them
has a clear meaning. volumev2, version='3' is just legit not a thing.
Needed-By: https://review.openstack.org/564494
Change-Id: Iec09bcb16d8e9b09e09bf12d03c2a55e679ad70c