Code review comment for lp:~mir-team/mir/revert-3098

From the discussion on the IRC, I don't believe probing logic is the problem, but care has to be taken when launching the nested server due to the known problem lp:1515558 ('--vt' switch needs to be used, if mesa-kms is desired).

In my local experiments on xenial desktop, with the '--vt' switch, everything works as expected. I suspect the crash seen in lp:1526209 may be due to something else. More investigation is needed.