test: new test, verify pre:post: scripts with optional env:file

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

test/skel/bin/post.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+marker="POST"
+# shellcheck disable=SC2154
+if [ -n "$baz" ]; then
+    marker=$baz
+fi
+
+echo "$marker" > /tmp/post

test/skel/bin/pre.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+marker="PRE"
+# shellcheck disable=SC2154
+if [ -n "$foo" ]; then
+    marker=$foo
+fi
+
+echo "$marker" > /tmp/pre

test/skel/etc/env

@@ -0,0 +1,5 @@
+# Some environments to be sourced by Finit services
+# and their pre:- and post:scripts
+
+foo=bar
+baz=qux