add option for removing cron provided by distro pkgs

[gmenuel]

Pull Request (PR) description

This PR aims at removing the system cron or systemd timer when the renew cron is managed by puppet (this doesn't handle certonly cron). If we don't do that on certains distro (for exemple Debian), a cron will be automaticaly added by the package and might renew the certificate before the puppet cron, and thus the puppet renew hooks won't be executed.

This Pull Request (PR) fixes the following issues

Fixes #164

[treydock]

@gmenuel Please address the merge conflicts.

[gmenuel]

I've updated the cron file name for freeBSD. I've don't have a freeBSD to test that it is correct (and I'm not particulary familiar with it) so if anyone can check that this is correct it would be great :)