Support for configuring inet_dist_listen_min and inet_dist_listen_max for firewalled nodes

For rabbitmq clusters deployed with a firewall in between (like in ec2), need the ability to specify a range of ports  that are permitted to be used for inter-communication so that they can be configured accordingly in the firewall.

According to http://www.rabbitmq.com/clustering.html, this is done by configuring the kernel parameters inet_dist_listen_min and inet_dist_listen_max.

The erlang configuration file is tricky to manage since the last item in an array should not end with a ",". So have set a dummy property at the end without a "," which is just to keep the template logic simple. Any suggestions to better handle this case are welcome.