The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/46d2e034e34927003989339244e5469c8042f625

commit 46d2e034e34927003989339244e5469c8042f625
Author: Roberto Carrillo <robertocn@google.com>
Date: Mon Jun 12 22:51:17 2017

[Findit] Cron job to run periodic bot update on swarmbucket.

This periodically runs the preemptive_bot_update recipe on idle bots in
the findit pool of swarmbucket hosts, to reduce the average time a
tryjob spends fetching code from a remote server.

R=chanli,stgao,lijeffrey
BUG= 730178 

Change-Id: Idb5823cccd9b46c24e892e4f7e20e641d154208e
Reviewed-on: https://chromium-review.googlesource.com/530085
Commit-Queue: Roberto Carrillo <robertocn@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>
Reviewed-by: Jeffrey Li <lijeffrey@chromium.org>

[add] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/handlers/test/periodic_bot_update_test.py
[modify] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/common/waterfall/buildbucket_client.py
[modify] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/waterfall/test/swarming_util_test.py
[modify] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/main.py
[modify] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/waterfall/swarming_util.py
[modify] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/cron.yaml
[add] https://crrev.com/46d2e034e34927003989339244e5469c8042f625/appengine/findit/handlers/periodic_bot_update.py