[cit] Use subprocess2 to properly sink stdout.
[cit] Use subprocess2 to properly sink stdout.

This should fix the "halts mid-way" symptoms observed on linux.

R=agable@chromium.org, 2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org

Bug: 782543
Change-Id: Ia5254b7f8e73b5646f2782e36acc52b4772b095e
Reviewed-on: https://chromium-review.googlesource.com/865821
Reviewed-by: Ryan Tseng <2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org>
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools