HDFS-5249. Fix dumper thread which may die silently. Contributed by Brandon Li

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1525770 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5251. Race between the initialization of NameNode and the http server. Contributed by Haohui Mai.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1525787 13f79535-47bb-0310-9956-ffa450edef68