svn merge -c 1532857 from trunk for HDFS-5283. Under construction blocks only inside snapshots should not be counted in safemode threshhold.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1532858 13f79535-47bb-0310-9956-ffa450edef68
svn merge -c 1532860 from trunk for adding TestOpenFilesWithSnapshot.java for HDFS-5283.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1532861 13f79535-47bb-0310-9956-ffa450edef68