Revert "GS Cache: using vpython"

This reverts commit f092e0629fbb3d2422c381324d056dadf035bac3.
The change to be reverted breaks provision.

BUG=chromium:840975,chromium:824580
TEST=None

Change-Id: I9002c4cf0026fee49b522527e626ec46c14c8b87
Reviewed-on: https://chromium-review.googlesource.com/1050749
Reviewed-by: Congbin Guo <guocb@chromium.org>
Reviewed-by: Ningning Xia <nxia@chromium.org>
Tested-by: Congbin Guo <guocb@chromium.org>
Commit-Queue: Congbin Guo <guocb@chromium.org>
7 files changed