[autotest] Add a dummy test for testbed.

This change also updates the special task control segments to support testbed.

BUG=chromium:574173
TEST=local run the dummy test.

Change-Id: I233511fa340050b74df3fdbcc76c4a408ded5fcf
Reviewed-on: https://chromium-review.googlesource.com/320204
Commit-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@google.com>
Reviewed-by: Simran Basi <sbasi@chromium.org>
7 files changed