This is needed since depot_tools may not be in PATH on LUCI bots. Using the copy
of depot_tools that contains the recipes is also incorrect as it is not
guaranteed to contain binaries that do not have corresponding recipe API, which
does not apply to script called from a recipe. This also protects our release
scripts from breaking due to arbitrary changes to depot_tools.

Chromium also pins depot_tools for similar reasons:
https://cs.chromium.org/chromium/src/DEPS?l=525&rcl=f24fa931ae08b0e42aae2d13034229088179da7f

R=machenbach@chromium.org

Bug: chromium:831171
Change-Id: I393052b1c489d25e2e3fa173149635448e9bd2dc
Reviewed-on: https://chromium-review.googlesource.com/1054676Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53179}