YARN-1889. In Fair Scheduler, avoid creating objects on each call to AppSchedulable comparator (Hong Zhiguo via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1583494 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5759. Remove unnecessary conf load in Limits (Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1583498 13f79535-47bb-0310-9956-ffa450edef68