Log subprocess output in run_perf_tests.py To aid with debugging a flaky hang listing tests on Android. Bug: chromium:1279512 Change-Id: Icbdf753e1e7c21ab766fdd5767ca05d07b66485b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3353760 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Yuly Novikov <ynovikov@chromium.org>