This change introduces a new option to define the region to which
the Barbican endpoint belongs. This is required if the deployment has
multiple regions and a single Keystone instance stores multiple
Barbican endpoints for different regions.
This change also ensures that the same interface and region are used
in endpoint detection and api version detection.
Change-Id: If2c0055d45922937e259a8f22f5879c9faa41e35
8c48341169