MQTT convert to async (#6064)

* Migrate mqtt to async

* address paulus comment / convert it complet async

* adress paulus comment / remove future

* Automation triggers should be async

* Fix MQTT async calls

* Show that event helpers are callbacks

* Fix tests

* Lint

homeassistant/components/automation/mqtt.py

@@ -4,6 +4,7 @@ Offer MQTT listening automation rules.
 For more details about this automation rule, please refer to the documentation
 at https://home-assistant.io/components/automation/#mqtt-trigger
 """
+import asyncio
 import json
 
 import voluptuous as vol
@@ -24,6 +25,7 @@ TRIGGER_SCHEMA = vol.Schema({
 })
 
 
+@asyncio.coroutine
 def async_trigger(hass, config, action):
     """Listen for state changes based on configuration."""
     topic = config.get(CONF_TOPIC)
@@ -49,4 +51,6 @@ def async_trigger(hass, config, action):
                 'trigger': data
             })
 
-    return mqtt.async_subscribe(hass, topic, mqtt_automation_listener)
+    remove = yield from mqtt.async_subscribe(
+        hass, topic, mqtt_automation_listener)
+    return remove