cleanup for nagios_nrpe_arguments

Hi @jwpari,

This pull request references https://github.com/rapid7/metasploit-framework/pull/1614 . I'm trying to do module cleanup with the hope it accelerates merging :) Please feel free to review and discuss anything, once you agree with the changes, feel free to land into your repo, and the original pull request https://github.com/rapid7/metasploit-framework/pull/1614 will be updated automatically. Thanks!