map docker container ports to allow usage of celery.contrib.rdb

http://docs.celeryproject.org/en/latest/reference/celery.contrib.rdb.html
allows you to remotely debug running celery tasks with:

    from celery.contrib import rdb
    rdb.set_trace()

this will bind a remote Python debugger on a random TCP port between
6899-6999, which you can telnet into for remote task debugging

tools/docker-compose.yml

@@ -9,11 +9,13 @@ services:
       RABBITMQ_USER: guest
       RABBITMQ_PASS: guest
       RABBITMQ_VHOST: /
+      CELERY_RDB_HOST: 0.0.0.0
     ports:
       - "8080:8080"
       - "5555:5555"
       - "8013:8013"
       - "8043:8043"
+      - "6899-6999:6899-6999"  # default port range for celery.contrib.rdb
     links:
       - postgres
       - memcached