Use uvloop for asyncio policy (#3417)

homeassistant/core.py

@@ -40,6 +40,12 @@ import homeassistant.util.dt as dt_util
 import homeassistant.util.location as location
 from homeassistant.util.unit_system import UnitSystem, METRIC_SYSTEM  # NOQA
 
+try:
+    import uvloop
+    asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())
+except ImportError:
+    pass
+
 DOMAIN = "homeassistant"
 
 # How often time_changed event should fire