(FACT-464) Improve support of Mandrake-derived osfamily detection

Previously, there were two issues:

* Mageia was not correctly separated from Mandriva as an
  operatingsystem
* All mandrake-derived distros showed up as "Linux" in osfamily

This adds a proper operatingsystem detection for Mageia and creates a
Mandrake osfamily for all mandrake-derived distros detected by the
operatingsystem fact.