HDFS-6057. DomainSocketWatcher.watcherThread should be marked as a daemon thread (cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1574789 13f79535-47bb-0310-9956-ffa450edef68
Merge r1574792 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1574794 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6061. Allow dfs.datanode.shared.file.descriptor.path to contain multiple entries and fall back when needed (cmccabe)

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