Moved CHANGES.txt entries to 2.6.2
Moved CHANGES.txt entries to 2.6.2

YARN-2019, YARN-4092, YARN-4101, YARN-4087, YARN-3727, YARN-4005,
YARN-3780, YARN-3802, YARN-3896, YARN-3554, YARN-3194, YARN-3798

(cherry picked from commit 14f0e2787c7c590d8ec1fc52f437866f34b098bd)

Conflicts:
	hadoop-yarn-project/CHANGES.txt

myeoje/PhillyYarn,mix/hadoop,mix/hadoop,mix/hadoop,myeoje/PhillyYarn,myeoje/PhillyYarn,myeoje/PhillyYarn,mix/hadoop,myeoje/PhillyYarn,mix/hadoop,myeoje/PhillyYarn,myeoje/PhillyYarn,mix/hadoop,mix/hadoop,mix/hadoop,myeoje/PhillyYarn