Import access module from keystoneclient to handle V3 endpoints

* service_catalog.py will be used only by nova(cinder.py), it will be removed if nova
uses access instead of service_catalog. Then service_catalog.py and
test_service_catalog.py will be removed from cinderclient if necessary.

* Some unit tests are modified.

* Because of JSON format's modification, functions that process cinder
credentials and cinder endpoints are changed.

* Add dependency for keystoneclient in requirements.txt.

Change-Id: Icf7badfdddcf5f55536d95db7242aff58aa34b6e
Closes-Bug: #1263876
bp: service-catalog
Merge "Import access module from keystoneclient to handle V3 endpoints"