chaos: Reference global AFE server to bypass sharded instances in local labs.

While here, removed function lock_webdriver_in_afe() as that is never called and
tests use allocate_webdriver_instance(). Also removed unused imports.

BUG=chromium:570498
TEST=Ran trybot; could lock packet_capture and webdriver
pre-cq-configs: mixed-wificell-pre-cq

Change-Id: Ie2d9e0588cb06eb85c4def558372ffbd375c9ef3
Reviewed-on: https://chromium-review.googlesource.com/322763
Commit-Ready: Tien Chang <tienchang@chromium.org>
Tested-by: Tien Chang <tienchang@chromium.org>
Reviewed-by: Tien Chang <tienchang@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
3 files changed