[autotest] Collect update engine log even if run_update failed.

BUG=chromium:279299
TEST=run_suite to force a machine install, interrupt the update by rebooting
DUT, confirm update_engine.log content is shown in autoserv.DEBUG

Change-Id: I97440face937a8c6bb4f009030aef01f02fe2f18
Reviewed-on: https://chromium-review.googlesource.com/167672
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
2 files changed