Implement a new mini cluster class for end users

Introduce a new TestingHBaseCluster for end users to start a mini hbase cluster in tests. After starting the cluster, you can create a Connection with the returned Configuration instance for accessing the cluster. Besides the mini hbase cluster, TestingHBaseCluster will also start a zookeeper cluster and dfs cluster. But you can not control the zookeeper and dfs cluster separately, as for end users, you do not need to test the behavior of HBase cluster when these systems are broken. We provide methods for start/stop master and region server, and also the whole hbase cluster. Notice that, we do not provide methods to get the address for masters and regionservers, or locate a region, you could use the Admin interface to do this.