test: improve cluster-disconnect-handles test

This commit fixes two issues in test-cluster-disconnect-handles:

1. If the master's TCP connection to the worker fails, the worker
process stays alive and causes many other tests that use the same
common port number to also fail (with EADDRINUSE).

2. One particular problem that can cause the master's TCP connection
to fail is attempting an IPv6 connection to the worker when no IPv6
network interfaces are available.

PR-URL: https://github.com/nodejs/node/pull/4084


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>