HDFS-5865. Update OfflineImageViewer document. Contributed by Akira Ajisaka.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1590100 13f79535-47bb-0310-9956-ffa450edef68
YARN-483. Improve documentation on log aggregation in yarn-default.xml (Akira Ajisaka via Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1590150 13f79535-47bb-0310-9956-ffa450edef68