Expose service catalog to interested parties.

Added ServiceCatalogerForIdentityV2 interface to allow interested
software access to the raw service catalog.  Note that the interface
supported must necessarily expose the specific version of Openstack
Identity API version, as V2 and V3 are completely incompatible with each
other.
Merge pull request #104 from rackspace/expose-v2-service-catalog

Expose service catalog to interested parties.