[autotest] Make lxc_functional_test.py runnable.

It never had a shebang line, so it always needed to be run as 'python
lxc_functional_test.py'.  Add a shebang line for convenience.

BUG=chromium:786179
TEST=lxc_functional_test.py

Change-Id: If30dd6a25a373562778a8d73a6eb5c4130492ee0
Reviewed-on: https://chromium-review.googlesource.com/775883
Reviewed-by: Dan Shi <dshi@google.com>
Tested-by: Ben Kwa <kenobi@chromium.org>
diff --git a/site_utils/lxc/lxc_functional_test.py b/site_utils/lxc/lxc_functional_test.py
index a958765..4bf41c2 100755
--- a/site_utils/lxc/lxc_functional_test.py
+++ b/site_utils/lxc/lxc_functional_test.py
@@ -1,3 +1,4 @@
+#!/usr/bin/python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.