YARN-169. Update log4j.appender.EventCounter to use org.apache.hadoop.log.metrics.EventCounter (Anthony Rojas via jeagles)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1489584 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-0.23' into branch-0.23-gd