[HBASE-8805] Add online configeration supporting and corresponding testcases

Summary: HRegion implements ConfigurationObserver, register/deregister from HRegionServer.configurationManager, testcases

Test Plan: Run testcase

Reviewers: gauravm, zelaine, liyintang

Reviewed By: liyintang

CC: mahesh, hbase-eng@

Differential Revision: https://phabricator.fb.com/D1067616

Task ID: 2977299

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1548981 13f79535-47bb-0310-9956-ffa450edef68