Add stub resize handler

For uninitialized console handlers, provide a stub
to do nothing on resize.

This avoids such a request crashing a shared websocket session.

confluent_server/confluent/consoleserver.py

@@ -175,6 +175,9 @@ class ConsoleHandler(object):
             self.connectstate = 'connecting'
             eventlet.spawn(self._connect)
 
+    def resize(self, width, height):
+        return None
+
     def _get_retry_time(self):
         clustsize = len(self.cfgmgr._cfgstore['nodes'])
         self._retrytime = self._retrytime * 2 + 1