test: report timeout in TapReporter

Be slightly more verbose in cases where tests time out.

PR-URL: https://github.com/nodejs/node/pull/2647


Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>