Otherwise bots with a low number of cores will hang trying to schedule
a mere 4 tasks.
This change allowing scheduling of an arbitrary number of test tasks,
the count was also augmented to better stress test the system.

Bug: chromium:805932
Change-Id: Ia10cd583c0675c256b4fd5d2765b50855d77a7f9
Reviewed-on: https://chromium-review.googlesource.com/895584
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51019}