indexName自动追加日期，可以自定义header头，改变时间，源码如下：
http://grepcode.com/file/repository.cloudera.com/content/repositories/releases/org.apache.flume.flume-ng-sinks/flume-ng-elasticsearch-sink/1.3.0-cdh4.3.0/org/apache/flume/sink/elasticsearch/AbstractElasticSearchIndexRequestBuilderFactory.java