Fix for #1847 cannot drain events for Redis. Closes #2827

celery/worker/loops.py

@@ -50,7 +50,8 @@ def asynloop(obj, connection, consumer, blueprint, hub, qos,
     # consumer.consume() may have prefetched up to our
     # limit - drain an event so we are in a clean state
     # prior to starting our event loop.
-    connection.drain_events()
+    if connection.transport.driver_type == 'amqp':
+        hub.call_soon(connection.drain_events)
 
     # FIXME: Use loop.run_forever
     # Tried and works, but no time to test properly before release.