add new script VolumeBalancerNew.java for hadoop 2.6+ to rebalance mu…

[kavnsir]

…ltiple disk data on a datanode

What changes were proposed in this pull request?

This PR proposes to support Hadoop 2.6+ for volume rebalancing

Since HDFS-6482, HDFS use the two-level directory structure for block storing, that is {subdir0 ~ subdir255} / {subdir0 ~ subdir255}, so we can move the same subdir between two volumes.

How was this patch tested?

This script has been used in product environment for volume rebalancing, and has a good performance.