Fix virtualbox build and reflector installation, as well as reflector-init.service

Created by: juadde

I wanted to investigate why reflector-init was not working with the latest boxes, and found that building the box failed. Pacman was failing to install reflector due to the missing --noconfirm, and virtualbox guest modules are now part of "linux" package directly, so there's no need to add them. I will investigate on the refector-init issue, it seems that for me reflector is trying to reach the mirror page before having DNS available.