sulogin: add multi console feature from SysVinit sulogin

sulogin: add multi console feature from SysVinit sulogin

Now after adding Conflicts=rescue.service to getty@.service and
serial-getty@.service and Conflicts=getty.target to rescue.target
all works with `systemctl rescue'.  Even adding init=/sbin/sulogin
to the kernels command line by using the `e' key in grub2 boot
menu works flawless.

This version is without the emergency code as I've this moved to
lib/console.c where it belongs to.

Signed-off-by: Werner Fink <werner@suse.de>