message: add a default erlang cookie.
diff: @@ -8,5 +8,7 @@ ADD enabled_plugins /etc/rabbitmq/enabled_plugins
  ADD rabbitmq.conf /etc/rabbitmq/rabbitmq.conf
  RUN chgrp 0 /etc/rabbitmq/rabbitmq.conf; chmod g+rw /etc/rabbitmq/rabbitmq.conf
  +ENV RABBITMQ_ERLANG_COOKIE=5188fd99edf19acfefcbb29a16f3d373aa01f66bfe89929852dfad2674d36af2
  +
  # this is only used in the cluster version
  ADD cluster-rabbit.sh /
  