Add the gifn-apply test tool

Add a tool that checks out the repositories mentioned in
a git-if-needed patch series, runs gif-it-needed, and performs
some checks on its operation. This tool will eventually be used in
a Zuul test job for this repository.

Change-Id: Id02fb7c21f5ab34d9639bf845fcc3961d929b13b
diff --git a/tools/git-if-needed/shellcheckrc b/tools/git-if-needed/shellcheckrc
index 2a4d199..9682ee0 100644
--- a/tools/git-if-needed/shellcheckrc
+++ b/tools/git-if-needed/shellcheckrc
@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: StorPool <support@storpool.com>
+# SPDX-License-Identifier: BSD-2-Clause
+
 shell=dash
 enable=all
 disable=SC2250