Add ulimit line to rabbit conf for controller nodes

An issue was discovered where rabbitmq running on a controller node with a large number of compute nodes could potentially open enough connections to hit the Max open files limit.

Attempted adjusting the limits for rabbitmq in /etc/security/limits.conf which did not work.  Per the following link, the open file limit sets for rabbitmq is, by default, set to 1024 on start and may be changed in the config file: http://www.rabbitmq.com/install-debian.html#debian-system-limits

This setting took in "rabbitmq-env.conf"