Add tests for domain users for trusts
Add tests for domain users for trusts

Users with any role on a domain have no ability to use trusts. That
privilege is only granted to project users, who may create trusts for
their own project and list and delete their own trusts, and system
users, who may audit and clean up trusts. This change adds tests to
verify that behavior.

Change-Id: I8404c062cc07ef83bf77fdd9178919aff0a0d6d5
Partial-bug: #1818850

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