Fix javadoc in MetadataDocument and ElasticsearchMetadataStorage.
https://github.com/cdapio/cdap/blob/develop/cdap-elastic/src/main/java/io/cdap/cdap/metadata/elastic/ElasticsearchMetadataStorage.java#L770
https://github.com/cdapio/cdap/blob/develop/cdap-elastic/src/main/java/io/cdap/cdap/metadata/elastic/MetadataDocument.java#L44