host-tools: use python2 explicitly for shebang

All of these host tools are apparently written for Python2,
not Python3.

Use 'python2' in the shebang line according to PEP 394
(https://www.python.org/dev/peps/pep-0394/).

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/py/test.py b/test/py/test.py
index 74e560a..4695079 100755
--- a/test/py/test.py
+++ b/test/py/test.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python2
 
 # Copyright (c) 2015 Stephen Warren
 # Copyright (c) 2015-2016, NVIDIA CORPORATION. All rights reserved.