Specify vpython in shebang for test

I run following commands to create this CL.
$ git grep -l 'env python' | fgrep _test.py | fgrep -v third_party | \
  xargs sed -i 's/env python/env vpython/g'
$ git cl format

This is preparation to re-land crrev.com/c/1862931

Change-Id: I383b0c4244cc45fafac3cb546c6ba7073c9fbd1a
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/1862934
Reviewed-by: Junji Watanabe <jwata@google.com>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@google.com>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
NOKEYCHECK=True
GitOrigin-RevId: a6ff7c549eba6b5ff03154602484bc5de2d1f991
diff --git a/tests/bootstrap_test.py b/tests/bootstrap_test.py
index 2ed5553..9129a52 100755
--- a/tests/bootstrap_test.py
+++ b/tests/bootstrap_test.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env vpython
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
diff --git a/tests/stream_test.py b/tests/stream_test.py
index b7f98bf..c3d54dd 100755
--- a/tests/stream_test.py
+++ b/tests/stream_test.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env vpython
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
diff --git a/tests/streamname_test.py b/tests/streamname_test.py
index 99f0323..fd41549 100755
--- a/tests/streamname_test.py
+++ b/tests/streamname_test.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env vpython
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
diff --git a/tests/varint_test.py b/tests/varint_test.py
index 0dbbf8d..527d7b0 100755
--- a/tests/varint_test.py
+++ b/tests/varint_test.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env vpython
 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.