Add unique_id to mqtt camera (#16569)

* Add unique_id to mqtt camera

* Remove whitespaces

* Add test for unique_id

* Add blank line

homeassistant/components/camera/mqtt.py

@@ -19,12 +19,14 @@ from homeassistant.helpers import config_validation as cv
 _LOGGER = logging.getLogger(__name__)
 
 CONF_TOPIC = 'topic'
+CONF_UNIQUE_ID = 'unique_id'
 DEFAULT_NAME = 'MQTT Camera'
 
 DEPENDENCIES = ['mqtt']
 
 PLATFORM_SCHEMA = PLATFORM_SCHEMA.extend({
     vol.Required(CONF_TOPIC): mqtt.valid_subscribe_topic,
+    vol.Optional(CONF_UNIQUE_ID): cv.string,
     vol.Optional(CONF_NAME, default=DEFAULT_NAME): cv.string
 })
 
@@ -38,6 +40,7 @@ def async_setup_platform(hass, config, async_add_entities,
 
     async_add_entities([MqttCamera(
         config.get(CONF_NAME),
+        config.get(CONF_UNIQUE_ID),
         config.get(CONF_TOPIC)
     )])
 
@@ -45,11 +48,12 @@ def async_setup_platform(hass, config, async_add_entities,
 class MqttCamera(Camera):
     """representation of a MQTT camera."""
 
-    def __init__(self, name, topic):
+    def __init__(self, name, unique_id, topic):
         """Initialize the MQTT Camera."""
         super().__init__()
 
         self._name = name
+        self._unique_id = unique_id
         self._topic = topic
         self._qos = 0
         self._last_image = None
@@ -64,6 +68,11 @@ class MqttCamera(Camera):
         """Return the name of this camera."""
         return self._name
 
+    @property
+    def unique_id(self):
+        """Return a unique ID."""
+        return self._unique_id
+
     @asyncio.coroutine
     def async_added_to_hass(self):
         """Subscribe MQTT events."""