use celery 3.x BROKER_URL

* Celery 4.x specifies the broker via CELERY_BROKER_URL. Since we are
now on 3.x, use 3.x way of specifying the broker via BROKER_URL

installer/openshift/templates/configmap.yml.j2

@@ -78,7 +78,7 @@ data:
             'PORT': "{{ pg_port }}",
         }
     }
-    CELERY_BROKER_URL = 'amqp://{}:{}@{}:{}/{}'.format(
+    BROKER_URL = 'amqp://{}:{}@{}:{}/{}'.format(
         "awx",
         "abcdefg",
         "localhost",
@@ -87,7 +87,7 @@ data:
     CHANNEL_LAYERS = {
         'default': {'BACKEND': 'asgi_amqp.AMQPChannelLayer',
                     'ROUTING': 'awx.main.routing.channel_routing',
-                    'CONFIG': {'url': CELERY_BROKER_URL}}
+                    'CONFIG': {'url': BROKER_URL}}
     }
     CACHES = {
         'default': {