Keystone should prevent duplicate roles from being created

Issue

• Since all of the policy authentication uses the role names, it should be a unique key in the database. This issue has been observed when attempting to create a heat stack.
• Getting errors similar to :

"The server could not comply with the request since it is either malformed or otherwise incorrect.", "code": 400, "error": {"message": "Missing required credential: roles [u'admin']",

2017-06-13 14:23:34.928 399855 WARNING keystone.common.wsgi [req-4638a94d-17c3-4920-a1a0-d684c87ce2cc 96c6f079d46043d3b7938a5a3245b6cb 66a3f06e6448441896c8f794e5ecd5a7 - default default] role admin is not defined