Update doc string for service disable

It should be "Disable" but not "Enable" in doc string when disable
a service.

Change-Id: I658090d4e218222c76947c37f340fb2ab7d26ce3
Update service function name for service enable

When testing the function of enabling a service, the function name
should be test_service_enable.

Change-Id: I951c94315392834250183e0219b32804e5d2de66
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
Updated from global requirements

Change-Id: Ib0922bbc1be3c8f738e547fe54a080036b072cdd
Merge "Update doc string for service disable"
Merge "Import access module from keystoneclient to handle V3 endpoints"
Merge "Update service function name for service enable"