Allow setting nofiles ulimt via an env variable

[gcbirzan]

This would allow helm/charts#5873 to be fixed. A similar fix was implemented for the bitnami image for helm/charts#3855.

[yosifkit]

This is already available via the docker run interface, so it is not necessary via an environment variable:

$ docker run -it --rm --ulimit nofile=1024 rabbitmq bash
root@9a784c3998c3:/# ulimit -n
1024
root@9a784c3998c3:/# exit

See kubernetes/kubernetes#3595 for Kubernetes support. Since Kubernetes does not support it, you could always change the command of the container:

$ docker run -it --rm rabbitmq bash -c 'ulimit -n && ulimit -n 1024 && ulimit -n'
1048576
1024
$ # so, something like this:
$ docker run -d rabbitmq bash -c 'ulimit -n 1024 && exec docker-entrypoint.sh rabbitmq'

[pniebylski-zilch]

It is needed if you want default behaviour and not always think about adding --ulimit flag to each docker build or docker run commands