USE local lock for buildbot_test_toolchain.

Currently the AFE lock machanism for our nightly test is broken,
we use local lock as a workaround for now.

BUG=chromium:762589
TEST=Generate the crosperf command in another simple python file
     with the same code. Run the generated command line on
     crotomation2 and it goes though the locking machine stage.

Change-Id: Icd3132bc383b63aab6d6f5237a04348f11d8726d
Reviewed-on: https://chromium-review.googlesource.com/653213


Commit-Ready: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Reviewed-by: Caroline Tice <cmtice@chromium.org>