Call a spade a spade

When run on FreeBSD, with os-release saying that this is a FreeBSD
system, since there's no distro-match it ends up being called a Linux.
This changes the fallback / generic return from bestDistroMatch()
to handle non-Linuxes (leaves space for haiku or openBSD).

- Installing system packages for freebsd...
   Installing packages for freebsd/12.0