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)

Microsoft-CISL/hadoop-prototype,zrccxyb62/hadoop,zrccxyb62/hadoop,Microsoft-CISL/hadoop-prototype,Microsoft-CISL/hadoop-prototype,Microsoft-CISL/hadoop-prototype,zrccxyb62/hadoop,zrccxyb62/hadoop,zrccxyb62/hadoop,Microsoft-CISL/hadoop-prototype,zrccxyb62/hadoop,zrccxyb62/hadoop,Microsoft-CISL/hadoop-prototype,Microsoft-CISL/hadoop-prototype,Microsoft-CISL/hadoop-prototype