I think for now, the right fix is to add a call to the label
verifier in server/control_segments/provision.  That'll make
labels get checked and updated often enough to be meaningful.
Provisioning is rare enough and expensive enough that adding in
the call there should be a tolerable expense, even if we find
it's not quite ideal.

> I think for now, the right fix is to add a call to the label
> verifier in server/control_segments/provision.  That'll make
> ...

Strictly speaking, I mean we should call host.update_labels(),
not the verifier.

We should probably also clean up by removing
server/hosts/label_verify.py.  It seems likely that the
verifier can't reliably meet our performance targets, so
we should give up this code as a bad bet.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/f866014d382863663794c43c7f0a1703d8563084

commit f866014d382863663794c43c7f0a1703d8563084
Author: Kevin Cheng <kevcheng@chromium.org>
Date: Fri Aug 12 17:17:41 2016

[autotest] Re-enable updating labels during provision.

We'll update the labels after every successful provision.  Also track
the duration of the label update time so we can see if it's taking too
long, it should take < 10 seconds.

Also delete the label verifier since we won't be using that anymore.

BUG= chromium:629216 
TEST=Tested a provision on a celes and it worked (added the labels and
provision succeeded).

Change-Id: Ifaf5372c586fcedfa8d6b6c6c8a775ce53566911
Reviewed-on: https://chromium-review.googlesource.com/368472
Commit-Ready: Kevin Cheng <kevcheng@chromium.org>
Tested-by: Kevin Cheng <kevcheng@chromium.org>
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>

[modify] https://crrev.com/f866014d382863663794c43c7f0a1703d8563084/server/hosts/cros_host.py
[modify] https://crrev.com/f866014d382863663794c43c7f0a1703d8563084/server/control_segments/provision
[modify] https://crrev.com/f866014d382863663794c43c7f0a1703d8563084/server/hosts/testbed.py
[delete] https://crrev.com/f6579937c953d9c6f72f8dcd9ed9f2003f7d2167/server/hosts/label_verify.py

just need a push to prod and monitor the duration of the label update.

Was this pushed to prod?

Suspect this is causing boards to be incorrectly relabeled, e.g. chromeos4-row3-rack10-host8:

https://pantheon.corp.google.com/storage/browser/chromeos-autotest-results/hosts/chromeos4-row3-rack10-host8/148208-provision/20162408000501/debug/
...
08/24 00:14:29.991 INFO |        base_label:0244| removing labels: ['board:veyron_mickey']
08/24 00:14:31.256 INFO |        base_label:0251| adding labels: ['board:veyron_mickey_1.8GHz_2GB', 'servo']
...

I filed Issue 640505 to track the label issue.