Set priority from message properties if not in delivery_info

Add contributor.

celery/worker/request.py

@@ -152,7 +152,8 @@ class Request(object):
             'delivery_info': {
                 'exchange': delivery_info.get('exchange'),
                 'routing_key': delivery_info.get('routing_key'),
-                'priority': delivery_info.get('priority'),
+                'priority': delivery_info.get('priority',
+                                              properties.get('priority')),
                 'redelivered': delivery_info.get('redelivered'),
             }