Switch Celery broker from RabbitMQ to Redis

This should work around a bug in Celery where long Celery tasks would
time out and be re-queued, causing an infinite loop.

See https://github.com/celery/celery/issues/3430 for more info.

pillar/config.py

@@ -195,7 +195,7 @@ BLENDER_CLOUD_ADDON_VERSION = '1.4'
 TLS_CERT_FILE = requests.certs.where()
 
 CELERY_BACKEND = 'redis://redis/1'
-CELERY_BROKER = 'amqp://guest:guest@rabbit//'
+CELERY_BROKER = 'redis://redis/2'
 
 # This configures the Celery task scheduler in such a way that we don't
 # have to import the pillar.celery.XXX modules. Remember to run