tests: connection refactor.

Hitching off what @ryanseys found in #137 and the [discussion that followed](https://github.com/GoogleCloudPlatform/gcloud-node/pull/137#discussion_r16784017), here's a bit of a refactoring of the queue behavior of connection. Instead of building our own, we can use the NodeWay:tm: with the built in event emitter.

I was also able to hopefully simplify some of the setting up of Connection instances in the test.