add additional DB retry logic to the callback receiver

initially, I implemented this for _only_ the task worker, but it's
probably needed for callback event workers, too

awx/main/dispatch/worker/base.py

@@ -7,6 +7,7 @@ import signal
 from uuid import UUID
 from Queue import Empty as QueueEmpty
 
+from django import db
 from kombu import Producer
 from kombu.mixins import ConsumerMixin
 
@@ -128,6 +129,10 @@ class BaseWorker(object):
                 logger.error("Exception on worker {}, restarting: ".format(idx) + str(e))
                 continue
             try:
+                for conn in db.connections.all():
+                    # If the database connection has a hiccup during the prior message, close it
+                    # so we can establish a new connection
+                    conn.close_if_unusable_or_obsolete()
                 self.perform_work(body, *args)
             finally:
                 if 'uuid' in body: