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This ports the wait_for_logs method from the Python script, and forwards
the pipe write fd to the Python script.

Change-Id: Ief54da136894cd13e0761b9755aa3c7d51fe17f8
Reviewed-on: https://chromium-review.googlesource.com/594807Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Erik Jensen <rkjnsn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491058}