rebooting the VM from inside leads to the VM being down. This is not good. we should figure out what's going on in there.
So I tried on builder2 (cause builder1 is currently running tests), and it work fine there. (I was watching over with virt-manager).
Nope, same for builder1. So either reboot work fine when done by me connected as root, or the problem was fixed.
Well, in that case, I'll call this fixed! :)