[depot_tools] Turn my_activity.py into a vpython script

Downside: the script now requires "-u user@chromium.org" or it results
in "error: USER is not set, please use -u".

Bug: 904604
Change-Id: I241ad440d0cf1a495ce6f57e48ed49d9d90a49d9
Reviewed-on: https://chromium-review.googlesource.com/c/1442851Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>

my_activity.py

-#!/usr/bin/env python
+#!/usr/bin/env vpython
 # Copyright (c) 2012 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.
@@ -21,6 +21,17 @@ Example:
 # check those details to determine if there was activity in the given period.
 # This means that query time scales mostly with (today() - begin).
 
+# [VPYTHON:BEGIN]
+# wheel: <
+#   name: "infra/python/wheels/python-dateutil-py2_py3"
+#   version: "version:2.7.3"
+# >
+# wheel: <
+#   name: "infra/python/wheels/six-py2_py3"
+#   version: "version:1.10.0"
+# >
+# [VPYTHON:END]
+
 import collections
 import contextlib
 from datetime import datetime