Criterion proposal - keyboard layouts

[drago01]

We currently don't have any explicit criterion that mandates that
keyboard layouts choose in the installer should work in the installed
system.
As a maintainer of one of the packages involved there
(system-setup-keyboard) I see such bugs in basically every release,
during the development cycle.

We should pay more attention to such issues as a system that uses a
different keyboard layout as the one physically present can not only
be very annoying (we shouldn't release in that state) but
can be useless when you have special characters in your password(s).
(Can't easily decrypt / login).

As seen in  https://lists.fedoraproject.org/pipermail/test/2011-March/097859.html
we do currently have a paragraph that mentions this but is IMO way to
vague.

So I propose something like: "The keyboard layout selected in the
installer must be in use after rebooting the installer (plymouth and
X)".