util/lint: Add check for the signed-off-by line

Gerrit will let you push a patch without a signed-off-by line,
although I believe it can't actually be merged.  Instead of catching
it either manually, or when the patch is attempting to be merged,
catch this in the jenkins builder.

Change-Id: I80161befa157266dd4e3209839a06ff398aab6bb
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/17941
Tested-by: build bot (Jenkins)
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

util/lint/lint-stable-020-signed-off-by

@@ -0,0 +1,23 @@
+#!/bin/sh
+# This file is part of the coreboot project.
+#
+# Copyright 2016 Google Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; version 2 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# DESCR: Check for a signed-off-by line on the latest git commit
+
+# This test is mainly for the jenkins server
+if [ -n "$(command -v git)" ] && [ -d .git ]; then
+	if [ -z "$(git log -n 1 | grep '[[:space:]]\+Signed-off-by: ')" ]; then
+		echo "No Signed-off-by line in commit message"
+	fi
+fi