Enable parsing of Identity Service V3 catalog.

In Keystone V3, the service catalog in the token response
has been split into multiple entries per service. This change
checks the version of the Identity Service and performs the
appropriate parsing of the catalog.

Core code for Keystone V3 authentication are in openstack_auth.

TODO: Move to auto-detection of API versions when it is available.

Implements blueprint login-domain-support

Change-Id: I69073e5744def037caf522b1123755668887cfd9
Merge "Enable parsing of Identity Service V3 catalog."