test: move dns test to test/internet

parallel/test-dns-cares-domains needs a working internet connection
to function (or a local DNS resolver that returns an answer quickly),
otherwise it times out.  Move it to test/internet.

PR-URL: https://github.com/nodejs/node/pull/5905


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