Remove all the unnecessary code and use the service catalog to retrieve the
endpoint url.
Update affected tests.
Depend on libcloud >= 0.12.4.
Inherit from the OpenStackDriverMixin and allow users to specify auth token by
passing ex_force_auth_token variable to the constructor.
Add a test for forcing auth token.
Merge pull request #25 from racker/allow_user_to_specify_auth_token

Allow user to pass force auth token
Merge pull request #24 from racker/use_service_catalog

Use service catalog