The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/aace272d58d38fc208e74e96382133a76071b676

commit aace272d58d38fc208e74e96382133a76071b676
Author: David Haddock <dhaddock@chromium.org>
Date: Thu Mar 15 22:27:39 2018

Add an autotest that updates, powerwashes, then does a rollback.

We have autotests for powerwash and rollback but not for this sequence
of steps which the test team has performed manually for ages.

Manual test case and result history:
https://testtracker.googleplex.com/testplans/testcase/detail/905705?id=450

BUG= chromium:817635 
TEST=autoupdate_Rollback.powerwash_before_rollback

Change-Id: I61eea7632c5ed3b8b225e4460d4cf06005682e21
Reviewed-on: https://chromium-review.googlesource.com/942369
Commit-Ready: David Haddock <dhaddock@chromium.org>
Tested-by: David Haddock <dhaddock@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>

[modify] https://crrev.com/aace272d58d38fc208e74e96382133a76071b676/server/site_tests/autoupdate_Rollback/autoupdate_Rollback.py
[add] https://crrev.com/aace272d58d38fc208e74e96382133a76071b676/server/site_tests/autoupdate_Rollback/control.powerwash_before_rollback

Looks mostly green:
https://stainless.corp.google.com/search?test=%5Eautoupdate%5C_Rollback%5C.powerwash%5C_before%5C_rollback%24&exclude_non_release=true&exclude_cts=true&col=build&row=model&view=matrix&first_date=2018-03-20&last_date=2018-03-26

I will follow up with fixes for failures in another bug if necessary