HDFS-7222. Expose DataNode network errors as a metric. (Charles Lamb via wang)

(cherry picked from commit 86cad007d7d6366b293bb9a073814889081c8662)
HDFS-7227. Fix findbugs warning about NP_DEREFERENCE_OF_READLINE_VALUE in SpanReceiverHost (cmccabe)
(cherry picked from commit 7ab754545dca16518e8fe9353ef69b77f365426b)
HDFS-7232. Populate hostname in httpfs audit log (Zoran Dimitrijevic via aw)
HDFS-7257. Add the time of last HA state transition to NN's /jmx page. Contributed by Charles Lamb.
HADOOP-11170. ZKDelegationTokenSecretManager fails to renewToken created by a peer. (Arun Suresh and Gregory Chanan via kasha)

(cherry picked from commit db45f047ab6b19d8a3e7752bb2cde10827cd8dad)
HDFS-7223. Tracing span description of IPC client is too long (iwasakims via cmccabe)
(cherry picked from commit 5b56ac4c72d69d1b3d6feec9d96c9d62eb02d28c)
HDFS-7243. HDFS concat operation should not be allowed in Encryption Zone. (clamb via yliu)
YARN-2209. Replaced AM resync/shutdown command with corresponding exceptions and made related MR changes. Contributed by Jian He.

(cherry picked from commit 0f3b6900be1a3b2e4624f31f84656f4a32dadce9)
Updated CHANGES.txt to move YARN-2682 to branch-2.6
(cherry picked from commit 071c925c7dffbb825884a5df5a0104e7793b30fc)
HDFS-7258. CacheReplicationMonitor rescan schedule log should use DEBUG level instead of INFO level. Contributed by Xiaoyu Yao.
Merge remote-tracking branch 'remotes/origin/branch-2' into branch-2