This is a partial revert of:
https://crrev.com/c/890938 and https://crrev.com/c/893982

Before this CL, the test runner blocked on ongoing tests in order to
process their results after an internal timeout. However, the logic
required for this feature was overly complicated and prevented an
acceptable implementation for fast aborts. Furthermore, also the fuzzers
suffered from timeouts on swarming due to hanging tests.

Instead, we now abort immediately on internal timeout (used on
fuzzers), SIGINT (Ctrl-C) and SIGTERM. Ongoing tests are immediately
terminated and their results are disregarded. On SIGTERM and SIGINT,
we return with non-zero exit codes, and zero on internal timeout.

This will also properly return json output, when the external hard
timeout is reached on swarming (causes SIGTERM).

TBR=sergiyb@chromium.org

Bug: v8:7423, chromium:813065
Change-Id: Ib20f835f58a0970693bdd3b21dc5d766d8e115d8
Reviewed-on: https://chromium-review.googlesource.com/924852Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51399}