overlay: ignition-ostree-firstboot-uuid: use metadata_csum_seed fs fe…

…ature

We're hitting issues in some cases where users are seeing the
`tune2fs -U random` on the /boot filesystem fail even though it's
ran directly after an `e2fsck`. To prevent needing a filesystem
check at all let's store the metadata checksum seed in the superblock
which will allow us to change the UUID without needing any filesystem
checks.

This was not possible before but we recently got a grub fix so that
having this filesystem feature enabled wouldn't cause grub2 to throw
an error.

- https://lists.gnu.org/archive/html/grub-devel/2021-06/msg00031.html

Fixes: coreos/fedora-coreos-tracker#735

overlay.d/05core/usr/lib/dracut/modules.d/40ignition-ostree/ignition-ostree-firstboot-uuid

@@ -27,10 +27,7 @@ esac
 
 if [ "${TYPE}" == "${orig_type}" ] && [ "${UUID}" == "${orig_uuid}" ]; then
   case "${TYPE}" in
-    # For now we need to fsck first, see https://github.com/coreos/coreos-assembler/pull/1452
-    # Basically we're not passing `metadata_csum_seed` as a mkfs.ext4 option
-    # because grub2 barfs on it.
-    ext4) e2fsck -fy "${target}" && tune2fs -U random "${target}" ;;
+    ext4) tune2fs -O metadata_csum_seed -U random "${target}" ;;
     xfs) xfs_admin -U generate "${target}" ;;
     *) echo "unexpected filesystem type ${TYPE}" 1>&2; exit 1 ;;
   esac