test__hub.py: actually make sure that hub is started before testing

greentest/test__hub.py

@@ -98,7 +98,7 @@ class TestShutdown(unittest.TestCase):
 
     def test(self):
         # make sure Hub is started. For the test case when hub is not started, see test_hub_shutdown.py
-
+        gevent.sleep(0)
         assert not gevent.hub.get_hub().dead
         self._shutdown()
         self.assert_no_hub()