Add scripts to backup/restore FS directory

This lets you save the state of things to more quickly test other
changes

(for example, run customize-inner, then backup, then run the
standalone_install scripts)

backup.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+. config || exit 0
+set -e
+
+echo Backing up filesystem...
+sudo rsync -a --delete ${FS} ${FS}.backup

restore.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+. config || exit 0
+set -e
+
+echo Restoring filesystem...
+sudo rsync -a --delete ${FS}.backup ${FS}