Fixed wrongly used assertEqual method

In several places, assertEqual is used the following way:
  assertEqual(observed, expected)
However, the correct way to use assertEqual is:
  assertEqual(expected, observed)

Change-Id: I5a7442f4adf98bf7bc73cef1d17d20da39d9a7f8
Closes-Bug: #1551861

watcher/tests/applier/messaging/test_trigger_action_plan_endpoint.py

@@ -38,4 +38,4 @@ class TestTriggerActionPlan(base.TestCase):
         action_plan_uuid = utils.generate_uuid()
         expected_uuid = self.endpoint.launch_action_plan(self.context,
                                                          action_plan_uuid)
-        self.assertEqual(action_plan_uuid, expected_uuid)
+        self.assertEqual(expected_uuid, action_plan_uuid)