docker: rabbitmq port exposure
docker: rabbitmq port exposure

* Amends RabbitMQ Docker container's port exposure to use the higher
  port (by adding 20000 to the usual port), so that one can run
  docker-based installation alongside OS-based installation without
  having to shut down any locally installed system services.

Signed-off-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio