Add a microcluster CLI option that launches a local Druid cluster with mostly default settings

* Makes heavy use of temporary directories
* Checks localhost:2181 for already launched zk instances, and launches a local zk server if nothing is bound to port 2181
* Launches a new JVM with really standard settings for each subtask
* Launches a temporary Derby DB to hold data.
* All things in this cluster are temporary and intended to die when the master JVM is shutdown.