[HBASE-8307] Adding a Histogram utility which captures data and creates a histogram

Author: manukranthk

Summary: This diff is to create a Histogram class which can be used to find the Percentile estimates of metrics in HBase. We can use this utility to calculate P99/P95 metrics of various metrics like latency etc.

Test Plan: Unit Testing

Reviewers: liyintang, rshroff, adela

Reviewed By: liyintang

CC: hbase-eng@

Differential Revision: https://phabricator.fb.com/D715751

Task ID: 2117219

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1466607 13f79535-47bb-0310-9956-ffa450edef68