Ensure any relevant tokens are revoked when a role is deleted

Add a controller class method to delete tokens for a role, along the
lines of those that exist for deleting tokens for user and project. Ensure
this is called for both the V2 and V3 delete_role APIs.

Fixes bug 1153645

Change-Id: I3c8d70eeb387a18c30df489142ea3aefc2224ae3
Merge "Ensure any relevant tokens are revoked when a role is deleted"