Smartly bind interfaces

[terinjokes]

Kappa should be bound to the external interface only, and couchdb to the internal interface on the same port. Tarball GETs can flow through Kappa just fine, and we think it would simplifies the port exports.

[totherik]

Hey, @terinjokes if there are any enhancements/bugs you find in kappa while sorting this out, please don't hesitate to file them. I'm really excited about docker-npmjs and we want to make sure firing up a private npm repo is as easy as possible.

[terinjokes]

Thanks.

Kappa doesn't rewrite the JSON responses from the private server, so in the current setup you have to expose both ports.

With this improvement, they'll be on the same port, so Kappa doesn't need to do any rewriting and only one port needs to be exposed.