Migrate to override_role for identity module (part 1)

Now that override_role has supplanted switch_role (which has
been deprecated) in [0], the RBAC tests need to switch to use
override_role.

This PS switches to override_role for the identity module. This
PS handles the first 10 modules for identity.

This PS also removes unnecessary indexing into response bodies.

[0] I670fba358bf321eae0d22d18cea6d2f530f00716

Partially Implements: blueprint rbac-utils-contextmanager

Change-Id: Ia80582119a98e63320859d8473987cdc2196d7e8
10 files changed