Add vpython.bat.

This brings us to parity with linux/mac.

R=dnj@chromium.org, vadimsh@chromium.org

Bug:
Change-Id: Iba112738db22ad594745735e7131801361cf8b50
Reviewed-on: https://chromium-review.googlesource.com/495547
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>

cipd_bin_setup.bat

+@echo off
+:: Copyright 2017 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.
+
+"%~dp0\cipd.bat" ensure -ensure-file "%~dp0\cipd_manifest.txt" -root "%~dp0\.cipd_bin"

vpython.bat

+@echo off
+:: Copyright 2017 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.
+
+call "%~dp0\cipd_bin_setup.bat"
+"%~dp0\.cipd_bin\vpython.exe" %*