iso-scan: Release resources on iso-scan boots with rd.live.ram

Unmounting the image iso, detaching its loop device, and unmounting
its parent partition can simplify installation to the parent disk.

Note that programs or scripts using the /run/initramfs/live mount
point will fail.

modules.d/90dmsquash-live/apply-live-updates.sh

@@ -18,3 +18,9 @@ if [ -h /dev/root ] && [ -d /run/initramfs/live/updates -o -d /updates ]; then
     done
     umount $NEWROOT/run
 fi
+# release resources on iso-scan boots with rd.live.ram
+if [ -d /run/initramfs/isoscan ] &&
+   [ -f /run/initramfs/squashed.img -o -f /run/initramfs/rootfs.img ]; then
+    umount --detach-loop /run/initramfs/live
+    umount /run/initramfs/isoscan
+fi