The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/a0bc466ddf08d786b316ffc39ac51a7cabf98c48

commit a0bc466ddf08d786b316ffc39ac51a7cabf98c48
Author: Roberto Carrillo <robertocn@google.com>
Date: Wed Nov 22 20:05:05 2017

[Findit] Support swarmbucket bots for flake tryjobs.

This change allows 2 things:
 - If a swarmbucket bot is configured, it will be returned by
 GetFlakeTrybot.
 - Instead of having a pair of swarmbucket_mastername/buildername keys
 we can simply set `'use_swarmbucket': True` to use the default
 hardcoded values.

R=chanli,lijeffrey
BUG= 787604 

Change-Id: I9aba4028aadf00a0332667ba794c5f89e5a1e13f
Reviewed-on: https://chromium-review.googlesource.com/783662
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: Jeffrey Li <lijeffrey@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>

[modify] https://crrev.com/a0bc466ddf08d786b316ffc39ac51a7cabf98c48/appengine/findit/waterfall/test/waterfall_config_test.py
[modify] https://crrev.com/a0bc466ddf08d786b316ffc39ac51a7cabf98c48/appengine/findit/waterfall/test/wf_testcase.py
[modify] https://crrev.com/a0bc466ddf08d786b316ffc39ac51a7cabf98c48/appengine/findit/waterfall/waterfall_config.py