YARN-2494. Added NodeLabels Manager internal API and implementation. Contributed by Wangda Tan.

(cherry picked from commit db7f1653198b950e89567c06898d64f6b930a0ee)
HDFS-7198. Fix "unchecked conversion" warning in DFSClient#getPathTraceScope (cmccabe)
(cherry picked from commit 1ceb3269337e321e352b7cd9f946c5c52dcfddfa)
HDFS-7209. Populate EDEK cache when creating encryption zone. (Yi Liu via wang)

(cherry picked from commit d3d3d47202a18749eeebec22db759c19dd3e232c)
HDFS-6252. Phase out the old web UI in HDFS. Contributed by Haohui Mai.
HDFS-6657. Remove link to 'Legacy UI' in trunk's Namenode UI. Contributed by Vinayakumar B.
YARN-2501. Enhanced AMRMClient library to support requests against node labels. Contributed by Wangda Tan.

(cherry picked from commit a5ec3d080978a67837946a991843a081ea712539)
HADOOP-11193. Fix uninitialized variables in NativeIO.c. Contributed by Xiaoyu Yao.
Merge remote-tracking branch 'remotes/origin/branch-2' into branch-2