To pick up support for "<project>:<bucket>/<builder>" syntax:
  https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1629989
  https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1632664

R=tandrii@chromium.org, maruel@chromium.org
BUG=966603

Change-Id: I870432a33c763c24591ee7e9eafe1154dda6df84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1635795Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>