[autotest] Acquire sonic hosts.

Sonic tests need a way to acquire hosts. Till crbug.com/337887 is completely
solved locking them should serve as a good intermediate solution.

TEST=Ran the sonic tests.
BUG=chromium:337887

Change-Id: I4b844e13565aa95de87f9d978908c0d0c1576a60
Reviewed-on: https://chromium-review.googlesource.com/184968
Tested-by: Prashanth B <beeps@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Kris Rambish <krisr@chromium.org>
Commit-Queue: Prashanth B <beeps@chromium.org>
8 files changed