getPrivateHostName returns the same thing as getPrivateIp. I would expect to get something like "ip-42-142-142-142.ec2.internal" as is reported by the AWS console.
Instance.getNodeMetadata().getHostname() returns the actual `hostname` as reported by the OS of the instance (which worked for me).
Not sure if this is expected behavior, or if it's a JCloud issue, or what. Feel free to mark invalid