test: add regression test for nghttp2 CVE-2018-1000168

PR-URL: https://github.com/nodejs-private/node-private/pull/117


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>