Set ES file descriptors via file in `limits.d`

This replaces the `bash` fu with an easier to read `file` resource.

No need for custom (and hard to read) `only_if` magic anymore
as Chef handles the idempotency itself.

This results in the following file:

    # cat /etc/security/limits.d/10-elasticsearch.conf
    elasticsearch     -    nofile    4000
    elasticsearch     -    memlock   unlimited

Tested on Debian 6