Use config region_name_for_services for rackspace clients

This deletes the region_name configuration option and replaces
uses with region_name_for_services.

There is no need for a different configuration option
for rackspace clients.

Change-Id: I6866026a0b9a1895b9b062e9c49e0fe54ec8e831
Merge "Use config region_name_for_services for rackspace clients"