test: fix test-net-socket-constructor

So it doesn't fail when creating a socket whose `fd` is already
being watched. Test that functionality now inside a cluster
worker.

Refs: https://github.com/libuv/libuv/pull/1851
Refs: https://github.com/libuv/libuv/issues/1897
PR-URL: https://github.com/nodejs/node/pull/21466


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>