Increase unit test coverage for rbac_utils.

With recent framework changes, need unit tests needed to be added
for full unit test coverage. This patch does just that.

Also made clear_rbac_roles a private class by prefixing it with
'_', and moved a validation method from __init__ which checked
whether admin_role_id or rbac_role_id were None to switch_role,
so that this check is performed more than just during the
initialization.

Change-Id: Iba261989d9cbffba9d33aec0d4f48c3fcc83092e
2 files changed