This adds flags to numfuzz for rerunning flaky tests and for storing
json test results. With those flags added, the infra-side can call
numfuzz with the same API as the standard test-runner.

TBR=sergiyb@chromium.org

Bug: v8:6917
Change-Id: I02d1cd02d90677c83f10e072383f3650c041cab1
Reviewed-on: https://chromium-review.googlesource.com/877890Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50753}