[433] Verify the existing daemon behaves correctly after multiple invocations

As per review, update the tests to ensure that the existing message
queue daemon still works even after we have had a failed attempt to
start a second copy of the daemon.

src/bin/msgq/tests/msgq_run_test.py

@@ -338,8 +338,11 @@ class MsgqRunTest(unittest.TestCase):
         self.__retcode = subprocess.call([MSGQ_PATH, '-s', SOCKET_PATH])
         self.assertNotEqual(self.__retcode, 0)
 
-        # Verify that the socket still exists
+        # Verify that the socket still exists and works. We re-call
+        # test_send_direct as a means of testing that the existing
+        # daemon is still behaving correctly.
         self.assertTrue (os.path.exists(SOCKET_PATH))
+        self.test_send_direct()
 
 if __name__ == '__main__':
     isc.log.init("msgq-tests")