tests: don't call Router.shutdown() twice.

Due to 497234e7 / issue #456.

tests/call_function_test.py

@@ -97,6 +97,7 @@ class CallFunctionTest(testlib.RouterMixin, testlib.TestCase):
         recv = self.local.call_async(time.sleep, 120)
         time.sleep(0.05)  # Ensure GIL is released
         self.broker.shutdown()
+        self.broker_shutdown = True
         exc = self.assertRaises(mitogen.core.ChannelError,
             lambda: recv.get())
         self.assertEquals(exc.args[0], self.router.respondent_disconnect_msg)

tests/testlib.py

@@ -388,12 +388,14 @@ class DockerizedSshDaemon(object):
 
 class BrokerMixin(object):
     broker_class = mitogen.master.Broker
+    broker_shutdown = False
 
     def setUp(self):
         super(BrokerMixin, self).setUp()
         self.broker = self.broker_class()
 
     def tearDown(self):
+        if not self.broker_shutdown:
             self.broker.shutdown()
         self.broker.join()
         super(BrokerMixin, self).tearDown()