This uses a temporary file in the mocked d8 script to let d8 flip
between FAIL and PASS on rerun.

This adds a separate test root with dedicated test suite for testing
flakes to no interfere with existing status file configs.

NOTRY=true

Bug: v8:6917
Change-Id: Id43753650195fb74cceb2a3ee9014100cabad546
Reviewed-on: https://chromium-review.googlesource.com/867917
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50621}