Add shebang line to dut_control.py

All python files that are expected to be executed should have this.
If you don't, you get something like this if you try to run:

$ ./servo/dut_control.py --help
./servo/dut_control.py: line 5: Client to control DUT hardware connected to servo debug board
: command not found

BUG=none
TEST=Ran ./servo/dut_control.py --help and saw no errors.

Change-Id: I7ab3ce6e5a6d3de2f42ec49dbc56c5cb3e9fc94c
Reviewed-on: http://gerrit.chromium.org/gerrit/5147
Reviewed-by: Todd Broch <tbroch@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
diff --git a/servo/dut_control.py b/servo/dut_control.py
index 59adfe9..971d815 100755
--- a/servo/dut_control.py
+++ b/servo/dut_control.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python
 # Copyright (c) 2011 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.