changing client_manager.region_name has no affect

Because of how openstackclient caches the various service clients, once a client is created for a given region, changing the region_name in the client manager does nothing if you want to ask for a new client for a different region.

As such the caching is silly for commands which may want to use the client_manager but need to switch regions in the course of the command operations.

With how keystoneauth1 handles sessions there is no longer any point in caching the clients. It is better to simply remove the cache, and just rebuild the clients fresh each time around the existing session.