Upgrading chaos app to python3 runtime BUG=chromium:1032597 Change-Id: Iaee3f06cfdfc881a75f654dd789bf729e9cd37bc Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/2399180 Reviewed-by: Dinesh Kumar Sunkara <dsunkara@google.com> Reviewed-by: Aashutosh Kalyankar <aashutoshk@chromium.org> Reviewed-by: Katherine Threlkeld <kathrelkeld@chromium.org> Tested-by: Aashutosh Kalyankar <aashutoshk@chromium.org> Auto-Submit: Aashutosh Kalyankar <aashutoshk@chromium.org> Commit-Queue: Aashutosh Kalyankar <aashutoshk@chromium.org>