update CDH version to 4.6.0 to solve leak in DFSClient (HDFS-5671)

[The socket leak in DFSInputStream](https://issues.apache.org/jira/browse/HDFS-5671) will cause a Presto node to finally run out of socket buffer space and freeze. [CDH 4.6.0](http://archive.cloudera.com/cdh4/cdh/4/hadoop-2.0.0-cdh4.6.0.CHANGES.txt) has included the patch for it.