use 'ps' output for Xorg and Xwayland. We'd need some new
openQA var to get this right by 'guessing', as it's vt1 for
Workstation when running live - so long as autologin worked -
but vt2 after install. We'd need a var or some other thing to
detect which case we're running in. LIVE doesn't do it, it's
set even when running a post-install test from a live image.
So instead let's just do it a bit more cleverly. This also
gives us a bit of insurance against changes in GDM, SDDM etc.
behaviour, so long as Xwayland or Xorg is running (and we can
add additional processes to the list, like gnome-shell, if
needed/appropriate). We assume the *final* listed process -
i.e. the most recently-started one - will be the desktop;
this covers gdm's behaviour of starting up on vt1 then running
the user session on vt2. We can make this function more complex
and add args if we ever get to the point where we have multi-
user tests running or anything (e.g. allow to pass a username
and only look for that user's processes).
Landing without review as this broke the live variant of the
test on Workstation in production (kinda not sure why it worked
in testing, or I didn't notice that it failed, but never mind).
I've tested it on staging.
ddc91efeff