test: mock the lookup function in parallel tests

These tests should not make any DNS calls. The lookup would fail
when the DNS requests are hijacked and time out instead of erroring
out.

PR-URL: https://github.com/nodejs/node/pull/17296
Refs: https://github.com/nodejs/help/issues/687


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>