test: consolidate http2 tests in one file

PR-URL: https://github.com/nodejs/node/pull/15624
Refs: https://github.com/nodejs/node/issues/14985


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>