HDFS-6482. Use block ID-based block layout on datanodes (James Thomas via Colin Patrick McCabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1615223 13f79535-47bb-0310-9956-ffa450edef68

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/impl/BlockPoolSlice.java
HDFS-6800. Support Datanode layout changes with rolling upgrade. (Contributed by James Thomas)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
HDFS-6981. Fix DN upgrade with layout version change. (Arpit Agarwal)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt