Comment 9 for bug 1305191

On the broken machine, please make sure to stop and undefine the
not-working vm, then

sudo stop libvirt-bin
sudo start libvirtbin

(make sure that you are on at least libvirt-bin version 1.2.2-0ubuntu11
and qemu-system-x86 2.0.0~rc1+dfsg-0ubuntu2 on that machine)