Bug#862562: debian-live: Log Out option don't work

[intrigeri <intrigeri@debian.org>]

Control: tag -1 + confirmed

syl:
> The menu on the top right offers an option to log out (in the submenu "Debian
> Live user"), it does not work and crash the system.

I can reproduce something similar with
debian-live-9.1.0-amd64-gnome.iso in a libvirt/QEMU VM with QXL
graphics: the graphical session disappears (as expected), and then
I very briefly see a GDM login screen and then I'm back to a text
mode console.

I suspect one can blame either GDM or the way it's configured (for
autologin) in our Live systems.

A Fedora 26 Live system exposes a similar, but different problem: upon
logout I'm back to the GDM login screen, I can click "Live System
User", I see a password prompt very quickly followed by the text
console, and very quickly again I'm back to the GDM login screen.

Cheers,
-- 
intrigeri