factory_install: Support Overlord.
Overlord is the new service (part of Umpire) that allows us to monitor
installation progress, especially for headless devices.
BUG=chromium:443972
TEST=Boots factory install shim & netboot on Overlord environment.
Change-Id: Ib4a1c30567b269872add608a80cdcb3e09b063a1
Reviewed-on: https://chromium-review.googlesource.com/247922
Reviewed-by: Wei-Ning Huang <wnhuang@chromium.org>
Tested-by: Wei-Ning Huang <wnhuang@chromium.org>
Commit-Queue: Hung-Te Lin <hungte@chromium.org>
3 files changed
