backups (tgz): work with a layout

this will allow us to place the localstorage directory in an arbitrary
location

src/scripts/mkdirvolume.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+set -eu -o pipefail
+
+if [[ ${EUID} -ne 0 ]]; then
+    echo "This script should be run as root." > /dev/stderr
+    exit 1
+fi
+
+if [[ $# -eq 0 ]]; then
+    echo "No arguments supplied"
+    exit 1
+fi
+
+if [[ "$1" == "--check" ]]; then
+    echo "OK"
+    exit 0
+fi
+
+volume_dir="$1"
+
+mkdir -p "${volume_dir}"
+