Reuse ClientHighAvailabilityServices when creating RestClusterClient

Currently, every newly built RestClusterClient will create a new ClientHighAvailabilityServices which is both unnecessary and resource consuming. For example, each ZooKeeperClientHAServices contains a ZKClient which holds a connection to ZK server and several related threads.

By reusing ClientHighAvailabilityServices across multiple RestClusterClient instances, we can save system resources(threads, connections), connection establish time and leader retrieval time.