ulimit simple implementation

Should solve it for CentOS (tested).

Neither /etc/pam.d/common-session, nor /etc/default/riak
are modified, but they might have to be; see
https://github.com/basho/riak-chef-cookbook/commit/41661c227e1a985a52ee87678a91588d05fbe372
and
http://docs.basho.com/riak/latest/cookbooks/Open-Files-Limit/.