gtest: output tap comments as yamlish

This makes yaml-ish parsers happy.
Note: gtest still seems to output the expected/result slightly
different making the full traceback less informational.

PR-URL: https://github.com/nodejs/node/pull/9262


Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Myles Borins <myles.borins@gmail.com>