Updates to demo component and platforms

homeassistant/components/sensor/demo.py

@@ -21,6 +21,11 @@ class DemoSensor(Device):
         self._state = state
         self._unit_of_measurement = unit_of_measurement
 
+    @property
+    def should_poll(self):
+        """ No polling needed for a demo sensor. """
+        return False
+
     @property
     def name(self):
         """ Returns the name of the device. """