Added Support for Restify Clients

The root cause of Restify not working with nock, was that it expects a `socket` event to be emitted before triggering a callback which calls `request.end()`.

https://github.com/mcavage/node-restify/blob/master/lib/clients/http_client.js#L243

I've solved this problem by emitting a fake `socket` event which plays nicely with Restify, along with adding several tests.