Set default input bus
vm-configurator: Default to PS2 input bus
Whenever the osinfo entry for the guest doesn't list a tablet device, we should default to PS2. When a tablet device is supported, the default input bus is set to USB.
This is the same behavior of virt-manager. See https://github.com/virt-manager/virt-manager/blob/master/virtinst/devices/input.py#L40
https://bugzilla.gnome.org/735768 Doesn't seem to be reproducible anymore.