deps: make gtest output tap

Teach gtest to produce TAP so we can integrate it better with our CI
tooling.

TAP is printed to stdout but it can also be written to file by passing
the `--gtest_output=tap:filename.tap` switch to cctest.

PR-URL: https://github.com/nodejs/node/pull/8034


Reviewed-By: James M Snell <jasnell@gmail.com>