YARN-2519. Credential Provider related unit tests failed on Windows. Contributed by Xiaoyu Yao.
HDFS-6898. DN must reserve space for a full block when an RBW block is created. (Contributed by Arpit Agarwal)
HDFS Credential Provider related Unit Test Failure. Contributed by Xiaoyu Yao.
Merge trunk into HDFS-6581

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/fsdataset/FsVolumeSpi.java
	hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDirectoryScanner.java