Fix compatibility issue with older Twisted in tests.

Older Twisted (18.4.0) returns TimeoutError instead of
ConnectingCancelledError when connection times out.
This change allows tests to be compatible with this behaviour.

Signed-off-by: Oleg Girko <ol@infoserver.lv>

tests/http/test_fedclient.py

@@ -49,7 +49,7 @@ class FederationClientTests(HomeserverTestCase):
     def test_client_never_connect(self):
         """
         If the HTTP request is not connected and is timed out, it'll give a
-        ConnectingCancelledError.
+        ConnectingCancelledError or TimeoutError.
         """
         d = self.cl._request("testserv:8008", "GET", "foo/bar", timeout=10000)
 
@@ -71,7 +71,7 @@ class FederationClientTests(HomeserverTestCase):
         self.reactor.advance(10.5)
         f = self.failureResultOf(d)
 
-        self.assertIsInstance(f.value, ConnectingCancelledError)
+        self.assertIsInstance(f.value, (ConnectingCancelledError, TimeoutError))
 
     def test_client_connect_no_response(self):
         """