Add RBAC test for communitize_image policy

This commit adds an RBAC test for communitize_image
policy, enforced via:

POST /v2/images with attribute visibility = community [0]

[0] https://github.com/openstack/glance/blob/b7c627ef68c303d4c3182c1a41b36185447039a3/doc/source/policies.rst

Change-Id: Icf2f14f8240389b17da4b92f6f0df168746d06b2
2 files changed