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/common/messaging/test_messaging_handler.py

@@ -70,8 +70,8 @@ class TestMessagingHandler(base.TestCase):
             serializer=None,
         )
 
-        self.assertEqual(handler.endpoints, [self.ENDPOINT])
+        self.assertEqual([self.ENDPOINT], handler.endpoints)
 
         handler.remove_endpoint(self.ENDPOINT)
 
-        self.assertEqual(handler.endpoints, [])
+        self.assertEqual([], handler.endpoints)