Lazy initialise the worker pool (#4110)

* Lazy initialise the worker pool

* Minimize pool initialization in core tests

* Fix tests on Python 3.4

* Remove passing in thread count to mock HASS

* Tests: Allow pool by default for threaded, disable for async

* Remove JobPriority for thread pool

* Fix wrong block_till_done

* EmulatedHue: Remove unused test code

* Zigbee: do not touch hass.pool

* Init loop in add_job

* Fix core test

* Fix random sensor test

homeassistant/components/sensor/zigbee.py

@@ -12,7 +12,6 @@ import voluptuous as vol
 from homeassistant.components import zigbee
 from homeassistant.components.zigbee import PLATFORM_SCHEMA
 from homeassistant.const import TEMP_CELSIUS
-from homeassistant.core import JobPriority
 from homeassistant.helpers.entity import Entity
 
 _LOGGER = logging.getLogger(__name__)
@@ -56,8 +55,7 @@ class ZigBeeTemperatureSensor(Entity):
         self._config = config
         self._temp = None
         # Get initial state
-        hass.pool.add_job(
-            JobPriority.EVENT_STATE, (self.update_ha_state, True))
+        hass.add_job(self.update_ha_state, True)
 
     @property
     def name(self):