tar2fs: wait a bit

Looks like there's a race condition somewhere: this script
will fail to clean up after itself when considerable background
load is inflicted upon the host it's running on (e.g. LA ~16
on a 8-core, single-disk system).

Note that this commit is NOT enough to win that race
but just a step in the right direction...

bin/tar2fs

@@ -129,7 +129,7 @@ exit_handler() {
 		umount ${BOOTFS:+"$BOOTFS"} "$ROOTFS"{/dev,/proc,/sys,}
 
 		if [ -n "$LOOPDEV" ]; then
-			kpartx -d "$LOOPDEV"
+			kpartx -d -s "$LOOPDEV"
 			losetup --detach "$LOOPDEV"
 		fi
 		rm -r -- "$ROOTFS"