More support for availability reporting on MQTT components (#11336)

* Abstract MQTT availability from individual components

- Moved availability topic and payloads to MQTT base schema.
- Updated components that already report availability:
  - Switch
  - Binary sensor
  - Cover

* Add availability reporting to additional MQTT components

- Light
- JSON light
- Template light
- Lock
- Fan
- HVAC
- Sensor
- Vacuum
- Alarm control panel

* Annotate MQTT platform coroutines

tests/components/light/test_mqtt_json.py

@@ -82,7 +82,8 @@ import unittest
 
 from homeassistant.setup import setup_component
 from homeassistant.const import (
-        STATE_ON, STATE_OFF, ATTR_ASSUMED_STATE, ATTR_SUPPORTED_FEATURES)
+    STATE_ON, STATE_OFF, STATE_UNAVAILABLE, ATTR_ASSUMED_STATE,
+    ATTR_SUPPORTED_FEATURES)
 import homeassistant.components.light as light
 from tests.common import (
     get_test_home_assistant, mock_mqtt_component, fire_mqtt_message,
@@ -472,3 +473,32 @@ class TestLightMQTTJSON(unittest.TestCase):
         state = self.hass.states.get('light.test')
         self.assertEqual(STATE_ON, state.state)
         self.assertEqual(255, state.attributes.get('white_value'))
+
+    def test_custom_availability_payload(self):
+        """Test availability by custom payload with defined topic."""
+        self.assertTrue(setup_component(self.hass, light.DOMAIN, {
+            light.DOMAIN: {
+                'platform': 'mqtt_json',
+                'name': 'test',
+                'state_topic': 'test_light_rgb',
+                'command_topic': 'test_light_rgb/set',
+                'availability_topic': 'availability-topic',
+                'payload_available': 'good',
+                'payload_not_available': 'nogood'
+            }
+        }))
+
+        state = self.hass.states.get('light.test')
+        self.assertEqual(STATE_UNAVAILABLE, state.state)
+
+        fire_mqtt_message(self.hass, 'availability-topic', 'good')
+        self.hass.block_till_done()
+
+        state = self.hass.states.get('light.test')
+        self.assertNotEqual(STATE_UNAVAILABLE, state.state)
+
+        fire_mqtt_message(self.hass, 'availability-topic', 'nogood')
+        self.hass.block_till_done()
+
+        state = self.hass.states.get('light.test')
+        self.assertEqual(STATE_UNAVAILABLE, state.state)