net: cleanup connect logic

Separates out the lookup logic for net.Socket. In the event
the `host` property is an IP address, the lookup is skipped.

PR-URL: https://github.com/iojs/io.js/pull/1505


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>