zdtm.sh: execute all zdtm test case for a defined commit

This functionality can help to test a patch set:
for i in `git rev-list HEAD~15..HEAD`; do
	./test/zdtm.sh -c $i || break;
done
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -415,6 +415,13 @@ while :; do
 		shift
 		continue
 	fi
+	if [ "$1" = "-c" ]; then
+		shift
+		checkout $1 || exit 1
+		shift
+		$TMP_TREE/test/zdtm.sh "$@"
+		exit
+	fi
 	break;
 done