Fix up a little test failure. Contributed by atm.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1500336 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9504 MetricsDynamicMBeanBase has concurrency issues in createMBeanInfo. Contributed by Liang Xie and Jason Lowe.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1500339 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5256 not needed in branch-1.  See r1500340 in branch-1.2

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1@1500342 13f79535-47bb-0310-9956-ffa450edef68