test: make test-net-connect-options-ipv6.js better

Improve the robustness of test-net-connect-options-ipv6.js

PPC Suse build team encountered intermittent failures related
to dns.  Improve test to make it more robust in the face
of intermittent dns issues.

PR-URL: https://github.com/nodejs/node/pull/5791


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