YARN-2632. Document NM Restart feature. Contributed by Junping Du and Vinod Kumar Vavilapalli
(cherry picked from commit 1e215e8ba2e801eb26f16c307daee756d6b2ca66)
YARN-2819. NPE in ATS Timeline Domains when upgrading from 2.4 to 2.6. Contributed by Zhijie Shen

(cherry picked from commit 4a114dd67aae83e5bb2d65470166de954acf36a2)