Add a test for modifying a role to set the name the same

There was no test that showed what happened when a role is modified
to have the same name. The test shows that when using the LDAP
assignment this request fails with a conflict error.

Change-Id: I40bb62200e79c8ff519e02facad042a657c26cae
Partial-Bug: #1401721
Merge "Add a test for modifying a role to set the name the same"