Update example platforms for async conventions (#1998)

source/developers/platform_example_light.markdown

@@ -76,11 +76,14 @@ class AwesomeLight(Light):
     def __init__(self, light):
         """Initialize an AwesomeLight."""
         self._light = light
+        self._name = light.name
+        self._state = None
+        self._brightness = None
 
     @property
     def name(self):
         """Return the display name of this light."""
-        return self._light.name
+        return self._name
 
     @property
     def brightness(self):
@@ -89,12 +92,12 @@ class AwesomeLight(Light):
         This method is optional. Removing it indicates to Home Assistant
         that brightness is not supported for this light.
         """
-        return self._light.brightness
+        return self._brightness
 
     @property
     def is_on(self):
         """Return true if light is on."""
-        return self._light.is_on()
+        return self._state
 
     def turn_on(self, **kwargs):
         """Instruct the light to turn on.
@@ -115,4 +118,6 @@ class AwesomeLight(Light):
         This is the only method that should fetch new data for Home Assistant.
         """
         self._light.update()
+        self._state = self._light.is_on()
+        self._brightness = self._light.brightness
 ```