By abstracting away vendor-dependent pattern matching for the linux code, we can
re-use that and be reasonably sure about OpenBSD machines being virtualised when
we can identify the undelrying virtualisation technology.
It remains to be solved how to tell if an OpenBSD machine is physical; in that
case previous cdist behaviour ("unknown") remains.
For NetBSD something similar to OpenBSD could be done, with different sysctls:
hw.machine and hw.model wary of adding those without testing though, so for
NetBSD previous cdist behaviour ("unknown") remains.
https://netbsd.gw.com/cgi-bin/man-cgi?sysctl+7.i386+NetBSD-9.0
More research is needed for {Net,Open}BSD support.
Indentation is left as-is for the linux code as I intend to simplify it in a
future MR, this way the diff is minimal.
