bad code is here: https://cs.corp.google.com/chromeos_public/chromite/cbuildbot/builders/simple_builders.py?q=if+suite_config.blocking+and+not+unibuild&sq=package:%5Echromeos_(internal%7Cpublic)$&g=0&l=124

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/e38f95cd801696ce8e1a3c9daee0880fce5c4cdd

commit e38f95cd801696ce8e1a3c9daee0880fce5c4cdd
Author: Xixuan Wu <xixuan@chromium.org>
Date: Sat Aug 04 08:59:45 2018

cbuildbot: Let blocking suite run first.

Provision suite is blocking suite. We want them to run and finish before
other suites, including unibuild.

It's not a problem in current system since if the DUTs are in
provisioning, scheduler will wait for them to finish then schedule.
However, when we move to skylab, swarming will return 'NO_RESOURCE'
immediately if no DUTs available:
e.g.
    https://chrome-swarming.appspot.com/task?id=3f179019f0108810&refresh=10

So if a suite want to be run in parallel, the correct way to do it is to
change its 'blocking' to False.

BUG= chromium:870046 
TEST=None

Change-Id: Iaf0d573de356f2d6829217a4567ac9e30bdb8844
Reviewed-on: https://chromium-review.googlesource.com/1162301
Commit-Ready: Xixuan Wu <xixuan@chromium.org>
Tested-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>

[modify] https://crrev.com/e38f95cd801696ce8e1a3c9daee0880fce5c4cdd/cbuildbot/builders/simple_builders.py

 Issue 803645  has been merged into this issue.