[XUbuntu] Disable guest session

To disable the guest session in XUbuntu, simply run:

sudo sh -c 'printf "[SeatDefaults]\nallow-guest=false\n" >/usr/share/lightdm/lightdm.conf.d/50-no-guest.conf'

this was tested under release 14.04 LTS.

To enable it again, either delete that file or remove the allow-guest=false line from it.

You may have to log out and log in again to see the changes applied.