test: add test for child_process benchmark

PR-URL: https://github.com/nodejs/node/pull/12326
Ref: https://github.com/nodejs/node/issues/12068


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>