make test_hub_join_timeout.py as flaky on windows

 C:\Python27\python.exe -u test_hub_join_timeout.py
  Traceback (most recent call last):
    File "test_hub_join_timeout.py", line 44, in <module>
      result = gevent.wait(timeout=10)
    File "C:\Python27\lib\contextlib.py", line 24, in __exit__
      self.gen.next()
    File "test_hub_join_timeout.py", line 22, in expected_time
      assert expected - fuzzy <= elapsed <= expected + fuzzy, 'Expected: %r; elapsed: %r' % (expected, elapsed)
  AssertionError: Expected: 0.1; elapsed: 0.15600013732910156

known_failures.py

@@ -54,6 +54,7 @@ test__execmodules.py
 test__socketpair.py
 test__makefile_ref.py
 FLAKY test__greenletset.py
+FLAKY test_hub_join_timeout.py
 '''.split('\n')
 
     if struct.calcsize('P') * 8 == 64:
@@ -74,7 +75,6 @@ FLAKY test__greenletset.py
             test__example_portforwarder.py
             test__socket_ex.py
             test__examples.py
-            test_hub_join_timeout.py
             test_subprocess.py
             test__issue600.py
             test__subprocess.py