OS Family Check Update - Release 2.0.0-411

Closes ticket https://github.com/NagiosEnterprises/nagiosvshell/issues/4.

Switched OS family identification from a `uname -a` check to a file existence check on `/etc/debian_version`. Default behavior is the same as before, choosing RedHat if check fails.

Thanks to [Esteban Monge](https://github.com/EstebanMonge) for bringing this issue up!