HDFS-5283. Under construction blocks only inside snapshots should not be counted in safemode threshhold.  Contributed by Vinay


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1532857 13f79535-47bb-0310-9956-ffa450edef68
Add TestOpenFilesWithSnapshot.java for HDFS-5283.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1532860 13f79535-47bb-0310-9956-ffa450edef68
Merge remote-tracking branch: upstream/trunk