test: fix parallel/test-net-socket-local-address
Fix flakiness where the client sometimes closed the server before the server had the chance to process the outstanding client connection. Make the server close itself instead.
Fixes: https://github.com/nodejs/node/issues/2475
R=@trott
CI: https://ci.nodejs.org/job/node-test-pull-request/885/ Stress test: https://ci.nodejs.org/job/node-stress-single-test/94/