autoinstall: move rootdelay=90 to Ubuntu-specific

systemd manages to do a reasonable job at booting with the dependencies
right, so there's no reason to wait 1½ minutes to boot. Probably :)
Let's try it for new installs.

Change-Id: I7d5b666727018995a61dd971be06aec50be35219
autoinstall: preseed popularity-contest

Change-Id: I6f0cff79238984df1406d73f3cbe1965a034bb0b