firstboot: make clear where the full screen console wizards end

firstboot: make clear where the full screen console wizards end

The three first boot screens are visually separated from the console
output before them via the "chome" and welcome strings and sufficient
whitespace. But so far they weren't from the output after them. This is
sometimes a big confusing. Let's add a bit of a separator between the
end and what comes next, too.

Just cosmetics, nothing else.