Add support for opendoas & void-linux to setup_tests script

[ernieIzde8ski]

Some systems (like mine) do not have sudo installed, but use the opendoas package to perform the same function.

The Void Linux package manager (xbps) was fairly easy to implement support for, though I restructured that part of code to do it.

I can think of one issue, but it was already present in the script in the first place: it's perfectly possible to have package managers from other distributions on your system, for managing chroot-like things. Maybe better OS detection or something more OS-independent would be better in the longterm.