Add nest hvac state (#4810)

* Add basic property details for Nest hvac_state

* Add the hvac_state sensor

* Update requirements and remove trailing whitespace

Clean up the multiline docstring

Adding a space between summary and description

* Removing the hvac_state as a property on the nest climate

* Update nest.py

homeassistant/components/sensor/nest.py

@@ -18,7 +18,8 @@ from homeassistant.const import (
 
 DEPENDENCIES = ['nest']
 SENSOR_TYPES = ['humidity',
-                'operation_mode']
+                'operation_mode',
+                'hvac_state']
 
 SENSOR_TYPES_DEPRECATED = ['last_ip',
                            'local_ip',