Move HADOOP-8934 in CHANGES.txt from 3.0.0 to 2.8.0.
Move HADOOP-8934 in CHANGES.txt from 3.0.0 to 2.8.0.

zjshen/hadoop-YARN-2928-POC,zjshen/hadoop-YARN-2928-POC,zjshen/hadoop-YARN-2928-POC,zjshen/hadoop-YARN-2928-POC,zjshen/hadoop-YARN-2928-POC,zjshen/hadoop-YARN-2928-POC,zjshen/hadoop-YARN-2928-POC