Add tests for domain users interacting with mappings
Add tests for domain users interacting with mappings

This commit introduces some tests that show how domain users are
expected to behave with the federated mapping API. A
subsequent patch will do the same for project users.

Change-Id: I743100a8e3a5c272a96e6679243d30199461958f
Related-Bug: 1804519

mahak/keystone,openstack/keystone,mahak/keystone,openstack/keystone,openstack/keystone,mahak/keystone