Force partuuid in /etc/default/grub.d/* instead of in /etc/default/grub

This prevents ucf questions upon installation of changed /etc/default/grub

live-build/ubuntu-cpc/functions

@@ -274,7 +274,8 @@ replace_grub_root_with_label() {
     CHROOT_ROOT="$1"
 
     # If boot by partuuid has been requested, don't override.
-    if grep -q ^GRUB_FORCE_PARTUUID= $CHROOT_ROOT/etc/default/grub; then
+    if [ -f $CHROOT_ROOT/etc/default/grub.d/40-partuuid ] && \
+           grep -q ^GRUB_FORCE_PARTUUID= $CHROOT_ROOT/etc/default/grub.d/40-partuuid; then
         return 0
     fi
     sed -i -e "s,root=[^ ]\+,root=LABEL=cloudimg-rootfs," \

live-build/ubuntu-cpc/hooks/032-disk-image.binary

@@ -118,7 +118,8 @@ if [ "${should_install_grub}" -eq 1 ]; then
 
 	if [ "$SUBPROJECT" = minimize ] && [ -n "$partuuid" ]; then
 		echo "partuuid found for root device; forcing it in Grub"
-		echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub
+		mkdir -p mountpoint/etc/default/grub.d
+		echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub.d/40-force-partuuid
 		chroot mountpoint update-grub
 	fi
 fi

live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary

@@ -66,7 +66,7 @@ install_grub() {
         # and 033-disk-image-uefi.binary.  We want to fix this to not
         # have initramfs-tools installed at all on these images.
         echo "partuuid found for root device; omitting initrd"
-        echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub
+        echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub.d/40-force-partuuid
     fi
 
     chroot mountpoint apt-get -y update