Update generic_thermostat.py

After _control_heating() is executed, current_operation() is correctly called but _is_device_active() still reports the old state if the heater switch, at least in my case. The resulting climate state is incorrect until the next refresh, which apparently occurs only when _sensor_changed() gets called (it can be minutes after).

I think the state of the heater switch should be forced to update at the end of  _control_heating(), but I don't know how to do that...
A simple sleep() fixes it, but obviously is just a temporary workaround, I'm not really expecting this PR to be actually committed, unless there's no other solution.

homeassistant/components/climate/generic_thermostat.py

@@ -16,6 +16,7 @@ from homeassistant.const import (
 from homeassistant.helpers import condition
 from homeassistant.helpers.event import track_state_change
 import homeassistant.helpers.config_validation as cv
+import time
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -222,6 +223,7 @@ class GenericThermostat(ClimateDevice):
                 if too_cold:
                     _LOGGER.info('Turning on heater %s', self.heater_entity_id)
                     switch.turn_on(self.hass, self.heater_entity_id)
+        time.sleep(.1)
 
     @property
     def _is_device_active(self):