Updated SleekTest.streamClose to check that the stream was actually started before closing it.

Updated tests for Iq stanzas to not start a stream for every test; tests now run a lot faster.
The call to streamClose must still be in the tearDown method to ensure it is called in the
case of an error.

tests/sleektest.py

@@ -258,7 +258,7 @@ class SleekTest(unittest.TestCase):
         self.checkPresence(data, sent, use_values)
 
     def streamClose(self):
-        if self.xmpp is not None:
+        if hasattr(self, 'xmpp') and self.xmpp is not None:
             self.xmpp.disconnect()
             self.xmpp.socket.recvData(self.xmpp.stream_footer)