Add new entry if entry is missing

Author: agners

buildroot-external/rootfs-overlay/usr/libexec/hassos-persists

@@ -30,7 +30,9 @@ elif [ -e /usr/bin/grub-editenv ]; then
 else
     if ! grep -q "systemd.machine_id=${MACHINE_ID}" /mnt/boot/cmdline.txt; then
         echo "[INFO] set machine-id to ${MACHINE_ID}"
-	sed -i "s/systemd.machine_id=[0-f]*/systemd.machine_id=${MACHINE_ID}/" /mnt/boot/cmdline.txt
+        if sed -i "s/systemd.machine_id=[0-f]*/systemd.machine_id=${MACHINE_ID}/" /mnt/boot/cmdline.txt; then
+            echo "systemd.machine_id=${MACHINE_ID}" > /mnt/boot/cmdline.txt
+        fi
     else
         echo "[INFO] machine-id is okay"
     fi