This makes the test runner and numfuzz share the same exit code behavior on
errors. This is needed as they also share the same infrastructure logic
to collect swarming tasks.

Bug: chromium:937228
Change-Id: I155b37c7b10dd22959a4dcf30bbd0321c452236b
Reviewed-on: https://chromium-review.googlesource.com/c/1495987Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59976}