test: temporarily back out changes from 11c1bae7

Temporarily revert the changes to test/ from commit 11c1bae7 ("lib: make
--debug-port work with cluster") to ease cherry-picks from joyent/node.

PR-URL: https://github.com/iojs/io.js/pull/501


Reviewed-By: Bert Belder <bertbelder@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>