Fix report mode and make it use testcase properties so statusfile
outcomes can be private.

Bug: v8:6917
Change-Id: Id38e89e0ba427c3bbb7ad12ba93e02beb7e46219
Reviewed-on: https://chromium-review.googlesource.com/833909
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50209}