HADOOP-10305. Add rpc.metrics.quantile.enable and rpc.metrics.percentiles.intervals to core-default.xml. Contributed by Akira Ajisaka.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1562660 13f79535-47bb-0310-9956-ffa450edef68