tests: Pass setUp arguments

ChannelPluginTestCase#setUp accepts the same parameters as its
super-method PluginTestCase#setUp, but it didn't pass the arguments down
the line.  Now it does.

src/test.py

@@ -486,7 +486,7 @@ class ChannelPluginTestCase(PluginTestCase):
         if not forceSetup and \
                 self.__class__ in (PluginTestCase, ChannelPluginTestCase):
             return
-        PluginTestCase.setUp(self)
+        PluginTestCase.setUp(self, nick, forceSetup)
         self.irc.feedMsg(ircmsgs.join(self.channel, prefix=self.prefix))
         m = self.irc.takeMsg()
         self.assertFalse(m is None, 'No message back from joining channel.')