[autotest] change python shebang to python2

Make sure all these scripts run as Python 2 since there is no support
for Python 3 in this code base.  This allows us to change the default
`python` to Python 3.

BUG=chromium:990593
TEST=CQ passes

Exempt-From-Owner-Approval: everyone has chimed in
Change-Id: I05321d92696f4550ced0741ead5023c8ec43c1e7
Reviewed-on: https://chromium-review.googlesource.com/1734588
Tested-by: Mike Frysinger <[email protected]>
Commit-Ready: ChromeOS CL Exonerator Bot <[email protected]>
Legacy-Commit-Queue: Commit Bot <[email protected]>
Reviewed-by: Vadim Bendebury <[email protected]>
Reviewed-by: Allen Li <[email protected]>
diff --git a/server/autoserv_utils.py b/server/autoserv_utils.py
index e019586..3889233 100644
--- a/server/autoserv_utils.py
+++ b/server/autoserv_utils.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python2
 # Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.