Added support for Ubuntu.

Replaced the 'operatingsystem' fact evaluated during the installation and configuration of Puppet with the 'osfamily' fact which makes this module also work on Ubuntu. Updated the README accordingly." -a
[ubuntu-support f39c233] Replaced the 'operatingsystem' fact evaluated during the installation and configuration of Puppet with the 'osfamily' fact which makes this module also work on Ubuntu. Updated the README accordingly.

Furthermore a bug in manifests/config.pp:88 was fixed: there was no case for 'undef' provided, leading to the error message: 'No matching value for selector param 'undef'.