Do not return identical error messages twice

e.g.

 $> curl -d '{"passwordCredentials": ...}' -H "Content-type: application/json" http://localhost:5000/v2.0/tokens

should return:

 {"badRequest": {"message": "Expecting auth", "code": "400"}}

not:

 {"badRequest": {"message": "Expecting auth or Expecting auth", "code": "400"}}

Change-Id: I76a432cbb4c964f4050b8596c773e0a553120ca3

keystone/controllers/auth.py

@@ -24,7 +24,10 @@ def authenticate(self, req):
                 result = config.SERVICE.authenticate_with_unscoped_token(
                     unscoped)
             except fault.BadRequestFault as e2:
-                raise fault.BadRequestFault(e1.msg + ' or ' + e2.msg)
+                if e1.msg == e2.msg:
+                    raise e1
+                else:
+                    raise fault.BadRequestFault(e1.msg + ' or ' + e2.msg)
 
         return utils.send_result(200, req, result)