test: fix flaky test-net-socket-local-address

Prior to this commit, the test was flaky because it was
executing the majority of its logic in a function called from
the client and multiple events on the server. This commit
simplifies the test by separating the server's connection and
listening events, and isolating the client logic.

Refs: https://github.com/nodejs/node/pull/4476
Refs: https://github.com/nodejs/node/pull/4644
PR-URL: https://github.com/nodejs/node/pull/4650


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