rename test_hub_shutdown.py to test_hub_join() and extend it a bit

--HG--
rename : greentest/test_hub_shutdown.py => greentest/test_hub_join.py

greentest/test_hub_join.py

+import gevent
+
+# hub.join() guarantees that loop has exited cleanly
+res = gevent.get_hub().join()
+assert res is True, res
+res = gevent.get_hub().join()
+assert res is True, res
+
+# but it is still possible to use gevent afterwards
+gevent.sleep(0.01)
+
+res = gevent.get_hub().join()
+assert res is True, res
+

greentest/test_hub_shutdown.py

-"""Tests that Hub.join() works even when hub is not yet started"""
-# rename to test_hub_join()?
-import gevent.hub
-res = gevent.hub.get_hub().join()
-assert res is True, res
-res = gevent.hub.get_hub().join()
-assert res is True, res