fsck root device: respect provided rootfstype

Created by: nightfog-git

By default, fsck determines filesystem type with a lookup of /etc/fstab. As for now it's empty in initramfs. So it defaults to ext2. That could (and actually do) damage the filesystem if it's not of an ext-family. The -a option is propagated to fsck.ext2 and it make it worse. The solution is fsck -t option. It will run the correct fsck.$rootfstype and not making harm with wrong one.