For step one I can make the error message better so that it prints the line from update_engine log saying we couldn't find a device to update from. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/6dc3930f84a0a61512aa9877dce6dddf085aacc9

commit 6dc3930f84a0a61512aa9877dce6dddf085aacc9
Author: David Haddock <dhaddock@chromium.org>
Date: Tue Jan 09 06:42:17 2018

Improve error messaging for P2P AU test.

The test is failing occasionally. This just improves the failure output
for one case.

BUG= chromium:799932 
TEST=autoupdate_FSI passes

Change-Id: I0d9ce7a314b8fd40e58180f14325cc70a14bfdb9
Reviewed-on: https://chromium-review.googlesource.com/854954
Commit-Ready: David Haddock <dhaddock@chromium.org>
Tested-by: David Haddock <dhaddock@chromium.org>
Reviewed-by: David Haddock <dhaddock@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>

[modify] https://crrev.com/6dc3930f84a0a61512aa9877dce6dddf085aacc9/server/site_tests/autoupdate_P2P/autoupdate_P2P.py

calling update_engine_client sometimes will fail. I need to add retries like other test code

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/9194e9cd44724d355621ea4f6bd84c133d03956c

commit 9194e9cd44724d355621ea4f6bd84c133d03956c
Author: David Haddock <dhaddock@chromium.org>
Date: Fri Jan 12 06:22:39 2018

Retry update_engine_client commands.

They can occassionally fail/timeout.
This was called out during original CL review but I forgot to address it.

BUG= chromium:799932 
TEST=autoupdate_P2P still passes.

Change-Id: I58501e60868b24f5a0ba2a3ec0ba1ca33798b7c5
Reviewed-on: https://chromium-review.googlesource.com/858417
Commit-Ready: David Haddock <dhaddock@chromium.org>
Tested-by: David Haddock <dhaddock@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>

[modify] https://crrev.com/9194e9cd44724d355621ea4f6bd84c133d03956c/server/site_tests/autoupdate_P2P/autoupdate_P2P.py