HDFS-7443. Datanode upgrade to BLOCKID_BASED_LAYOUT fails if duplicate block files are present in the same volume (cmccabe)
(cherry picked from commit 8fa265a290792ff42635ff9b42416c634f88bdf3)

Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataStorage.java