cleanup tests for keystone.common.cache

[Morgan Fainberg]

Cleanup and expand tests for keystone.common.cache to ensure all aspects are covered within the unit tests.

* The noop backend should have validation of methods
* Minor restructuring of the IsolationProxy to be more streamlined
* Add test to verify global toggle
* Add test to verify exception is raised when non-cache region is "configured"
* Validation of the debug proxy (data is not mangled in use).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/44408

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/44408
Committed: http://github.com/openstack/keystone/commit/90881278a11e4c6e6bd10cf07d3749c2491c5faf
Submitter: Jenkins
Branch: master

commit 90881278a11e4c6e6bd10cf07d3749c2491c5faf
Author: Morgan Fainberg <email address hidden>
Date: Thu Aug 29 23:13:52 2013 -0700

    Cleanup cache layer tests

    Simple cleanup of keystone/tests/test_cache.py. Added the following
    tests:

    * Global Should Cache Toggle
    * Configure Non-CacheRegion object raises Validation Error
    * Cache Debug Proxy doesn't mangle data / raise exceptions
    * Cache Noop Backend, in-fact, does nothing.

    Isolation proxy un-used methods removed.

    closes-bug: 1218743
    Change-Id: Id980a9bff554c72a02461cecbcb533466225a701