HADOOP-9964. Fix deadlocks in TestHttpServer by synchronize ReflectionUtils.printThreadInfo. (Junping Du via llu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1527651 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5230. Merging change r1527726 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1527741 13f79535-47bb-0310-9956-ffa450edef68