cbuildbot: Use buildbucket for remote tryjobs by default.

Remove --use-buildbucket option, and replace it with
--do-not-use-buildbucket option.

We want to use bucketbucket to schedule all tryjobs by default. We
haven't been able to find out for certain if there is anyone who needs
buildbucket permissions for this that doesn't already have them,
so.... let's find out!

A PSA has been sent out asking for feedback from anyone required to
use --do-not-use-buildbucket to run a tryjob.

This CL was submitted as CL:462518, and reverted as CL:464309.

BUG=chromium:671848
TEST=run_tests

Change-Id: I92f9137aa7cd4807a2b9006f357bf2189c2c0767
Reviewed-on: https://chromium-review.googlesource.com/465488
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Ningning Xia <nxia@chromium.org>
2 files changed