tools: show stdout/stderr for timed out tests

When a test times out, the contents of stdout and stderr can often be
highly valuable in debugging. Provide that information.

Refs: https://github.com/nodejs/node/issues/19906#issuecomment-382073888

PR-URL: https://github.com/nodejs/node/pull/20260


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>