lib: make debug client connect to 127.0.0.1

On machines without network connectivity, a DNS lookup for 'localhost'
may fail.  Connect to 127.0.0.1 to skip the host resolve step.

Fixes: https://github.com/iojs/io.js/issues/726
PR-URL: https://github.com/iojs/io.js/pull/741


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