HDFS-7154. Fix returning value of starting reconfiguration task (Lei Xu via Colin P. McCabe)
(cherry picked from commit 7aab5fa1bd9386b036af45cd8206622a4555d74a)
(cherry picked from commit 8c3b007236e01c7ad4922d1bf611e68d09adcfa8)
YARN-2709. Made timeline client getDelegationToken API retry if ConnectException happens. Contributed by Li Lu.

(cherry picked from commit b2942762d7f76d510ece5621c71116346a6b12f6)
YARN-2715. Fixed ResourceManager to respect common configurations for proxy users/groups beyond just the YARN level config. Contributed by Zhijie Shen.

(cherry picked from commit c0e034336c85296be6f549d88d137fb2b2b79a15)