Add utilities for ostree-based rootfs check

Need to include `fsck` and `fsck.ext4` utils explicitly since there is
no image and partitioning during `ostree-commit` recipe to trigger the
default mechanism provided by `mkinitramfs` scripts.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

overlays/ostree/usr/share/initramfs-tools/hooks/rootfsck

+#!/bin/sh
+
+# Copy utilities for root filesystem check in initramfs
+
+PREREQ=""
+
+prereqs()
+{
+        echo "$PREREQ"
+}
+
+case $1 in
+prereqs)
+        prereqs
+        exit 0
+        ;;
+esac
+
+. /usr/share/initramfs-tools/hook-functions
+
+copy_exec /sbin/fsck
+copy_exec /sbin/logsave
+copy_exec /sbin/fsck.ext4