HDFS-3429. DataNode reads checksums even if client does not need them. Contributed by Todd Lipcon.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433116 13f79535-47bb-0310-9956-ffa450edef68
Merge -c 1433138 from trunk to branch-2 to fix YARN-330. Fix flakey test: TestNodeManagerShutdown#testKillContainersOnShutdown. Contributed by Sandy Ryza

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433147 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4364. GetLinkTargetResponseProto does not handle null path. Contributed by Suresh Srinivas.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433202 13f79535-47bb-0310-9956-ffa450edef68