Fix for ember server --port

Fixes #208

This commit introduces `rewire`, DI library for node.

In order to test `server` command, we need to stub out the
[adapter](https://github.com/stefanpenner/ember-cli/blob/master/lib/commands/server.js#L36). 
But because we're testing `server` command in isolation, there's no way for us
to stub it out from outside (pass a stubbed value to the command itself for
example). Hence the DI.