Made the test runner be aware of differing configurations for Riak

I've preserved the original usage for running the tests, so that you can still do:

```zsh
rake test
```

However, since I run a Riak cluster mostly on the VMs through Vagrant, I needed to have the ability to pass the host and port in to the runner. The alternative usage with this pull request is:

```zsh
rake "test[33.33.33.11, 8111]"
```

The first parameter is the host, second the port.