Set client_id to None when none is specified

mqtt_sensord/mqtt_sensord.py

@@ -19,7 +19,7 @@ def main():
     if 'client_id' in config['mqtt']:
         client_id = config['mqtt']['client_id']
     else:
-        client_id = config['host']['name']
+        client_id = None
 
     mqtt = MQTTClient(mcfg['host'], mcfg['user'], mcfg['password'], client_id)
     mqtt_topic = mcfg['sensor_topic']