Modify the message of ERROR in stack_cancel_update()

Difficult to understand the ERROR.

TrivialFix

Change-Id: Idb19dc95ddb0c74915d9dfd28c1c20e122a7d217
Closes-Bug: #1555425

heat/engine/service.py

@@ -1092,8 +1092,9 @@ class EngineService(service.Service):
         current_stack = parser.Stack.load(cnxt, stack=db_stack)
         if current_stack.state != (current_stack.UPDATE,
                                    current_stack.IN_PROGRESS):
+            state = '_'.join(current_stack.state)
             msg = _("Cancelling update when stack is %s"
-                    ) % str(current_stack.state)
+                    ) % str(state)
             raise exception.NotSupported(feature=msg)
         LOG.info(_LI('Starting cancel of updating stack %s'), db_stack.name)
         # stop the running update and take the lock

heat/tests/engine/service/test_stack_update.py

@@ -407,7 +407,7 @@ class ServiceStackUpdateTest(common.HeatTestCase):
 
         self.assertEqual(exception.NotSupported, ex.exc_info[0])
         self.assertIn("Cancelling update when stack is "
-                      "('UPDATE', 'COMPLETE')",
+                      "UPDATE_COMPLETE",
                       six.text_type(ex.exc_info[1]))
 
     @mock.patch.object(stack_object.Stack, 'count_total_resources')