svn merge -c 1547173 merging from trunk to branch-2 to fix: HDFS-5557. Write pipeline recovery for the last packet in the block may cause rejection of valid replicas.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1547179 13f79535-47bb-0310-9956-ffa450edef68