WebHdfs client cannot communicate with older WebHdfs servers post HDFS-5306

HDFS-5306 introduced the field infoSecurePort to the DatanodeIDProto PB definition and made it optional for compatibility purposes. However, we don't correctly the handle the case when this field is not present when deserializing the response from a WebHdfs request. This results in an NPE at the client when this occurs.