Allow for absolute pathing to adapters for testing

I've been writing my own test adapters in separate hubot-scripts. The only way to bang on an adapter is to make it a separate npm package or drop it in hubot. This allows for full paths to adapters to be loaded.
I'm using it like [this](https://github.com/atmos/hubot-deploy/blob/master/test/index_test.coffee#L12-L14).