Add RBAC tests for v3 auth policy actions

Implements RBAC tests for v3 auth-related policy actions contained
in [0]. But since the Tempest identity v3 client currently only
has an endpoint for list_auth_projects [1], this patch only adds an
RBAC test for identity:get_auth_projects.

Once the other endpoints (show_auth_catalog and list_auth_domains)
are added to the Tempest client, then the remaining tests can be
added in a follow-up patch.

[0] https://github.com/openstack/keystone/blob/master/keystone/common/policies/auth.py
[1] https://github.com/openstack/tempest/blob/master/tempest/lib/services/identity/v3/identity_client.py

Change-Id: I002acfe760aeaab6d4618d366a2da522c6a27695
Partial-Bug: #1687317
2 files changed