Add ulimit nofile config for rabbitmq

In larger deployments the rabbitmq user will run out of file descriptors
due to the number of connections it opens. This change allows you to
modify the maximum number of file descriptors the user can have.

Change-Id: Ic691fd68c3397d392fd4a9db1ee672b1eae77b6d
Merge "Add ulimit nofile config for rabbitmq"