Fix BlacklistQueueTest on macOS

18:50:50 [OSXSLAVE] [INFO]      [exec] self = <tests.test_blacklist_queue.BlacklistQueueTest testMethod=testDelay>
18:50:50 [OSXSLAVE] [INFO]      [exec]     def testDelay(self):
18:50:50 [OSXSLAVE] [INFO]      [exec]         sleep_time = 3
18:50:50 [OSXSLAVE] [INFO]      [exec]         # Push two items with a delay of 1s
18:50:50 [OSXSLAVE] [INFO]      [exec]         queue = BlacklistQueue(delay=1)
18:50:50 [OSXSLAVE] [INFO]      [exec]         queue.push(1, "Item1")
18:50:50 [OSXSLAVE] [INFO]      [exec]         queue.push(2, "Item2")
18:50:50 [OSXSLAVE] [INFO]      [exec]         # Verify no item is returned back before 1s
18:50:50 [OSXSLAVE] [INFO]      [exec]         item = queue.get()
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertIsNone(item)
18:50:50 [OSXSLAVE] [INFO]      [exec]         sleep(sleep_time)
18:50:50 [OSXSLAVE] [INFO]      [exec]         # Verfiy we get the two items now
18:50:50 [OSXSLAVE] [INFO]      [exec]         item = queue.get()
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertIsNotNone(item)
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item.get(), "Item1")
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item.get_id(), 1)
18:50:50 [OSXSLAVE] [INFO]      [exec]         item = queue.get()
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertIsNotNone(item)
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item.get(), "Item2")
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item.get_id(), 2)
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item._count, 1)
18:50:50 [OSXSLAVE] [INFO]      [exec]         # Repush item without increasing delay
18:50:50 [OSXSLAVE] [INFO]      [exec]         queue.repush(item, increase_wait=False)
18:50:50 [OSXSLAVE] [INFO]      [exec]         item = queue.get()
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertIsNone(item)
18:50:50 [OSXSLAVE] [INFO]      [exec]         sleep(sleep_time)
18:50:50 [OSXSLAVE] [INFO]      [exec]         # We should get the repushed item after 1s wait
18:50:50 [OSXSLAVE] [INFO]      [exec]         item = queue.get()
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertIsNotNone(item)
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item.get(), "Item2")
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item.get_id(), 2)
18:50:50 [OSXSLAVE] [INFO]      [exec]         self.assertEqual(item._count, 2)
18:50:50 [OSXSLAVE] [INFO]      [exec]         # Repush item with increase
18:50:50 [OSXSLAVE] [INFO]      [exec]         queue.repush(item, increase_wait=True)
18:50:50 [OSXSLAVE] [INFO]      [exec]         sleep(sleep_time)
18:50:50 [OSXSLAVE] [INFO]      [exec]         item = queue.get()
18:50:50 [OSXSLAVE] [INFO]      [exec] >       self.assertIsNone(item)
18:50:50 [OSXSLAVE] [INFO]      [exec] item       = <nxdrive.engine.blacklist_queue.BlacklistItem object at 0x113b8acd0>
18:50:50 [OSXSLAVE] [INFO]      [exec] queue      = <nxdrive.engine.blacklist_queue.BlacklistQueue object at 0x113b8a810>
18:50:50 [OSXSLAVE] [INFO]      [exec] self       = <tests.test_blacklist_queue.BlacklistQueueTest testMethod=testDelay>
18:50:50 [OSXSLAVE] [INFO]      [exec] sleep_time = 3
18:50:50 [OSXSLAVE] [INFO]      [exec] nuxeo-drive-client/tests/test_blacklist_queue.py:48: