Only support the run_topic logic on the MQTT plugin.

Plugins that extend `MqttPlugin` shouldn't run messages as
requests, even if the parent MQTT plugin is configured to
do so.

platypush/plugins/mqtt/__init__.py

@@ -137,7 +137,7 @@ class MqttPlugin(RunnablePlugin):
         self.client_id = client_id or str(Config.get('device_id'))
         self.run_topic = (
             f'{run_topic_prefix}/{Config.get("device_id")}'
-            if run_topic_prefix
+            if type(self) == MqttPlugin and run_topic_prefix
             else None
         )