HDFS-6114. Block Scan log rolling will never happen if blocks written continuously leading to huge size of dncp_block_verification.log.curr (vinayakumarb via cmccabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1612944 13f79535-47bb-0310-9956-ffa450edef68