Fix mqtt prefix handling on thermostat worker

mqtt.py

@@ -59,6 +59,8 @@ class MqttClient:
     self.mqttc.connect(self.hostname, port=self.port)
 
     for topic, callback in callbacks:
+      if self.topic_prefix is not None:
+        topic = "{}/{}".format(self.topic_prefix, topic)
       self.mqttc.message_callback_add(topic, callback)
       self.mqttc.subscribe(topic)
 

workers/thermostat.py

@@ -71,7 +71,9 @@ class ThermostatWorker(BaseWorker):
     return ret
 
   def on_command(self, topic, value):
-    _, device_name, method, _ = topic.split('/')
+    if self.topic_prefix is not None:
+      _, device_name, method, _ = topic[len(self.topic_prefix+"/"):].split('/')
+
     thermostat = self.devices[device_name]
 
     value = value.decode('utf-8')