Test Runner: More misc improvements. - reduces default batch size from 1000 -> 256 - reduces default max processes to a max of 16 - stripes tests when in bot mode - prints less spam when waiting for child processes The striping and smaller batch size can help with slow tests. The max process limit seemed to prevent errors on Linux. Bug: angleproject:3162 Change-Id: Ibed89ca35db54c62ec8ed63b32bc5aed916faec9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2447037 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>