[HBASE-8576] - Make server side profiling online configurable

Author: zelaine

Summary: Make the parameter to enable/disable server side profiling configurable online.

Test Plan:
Added new unit test case.  Ran unit tests.  Got failures, but they were
similar to the ones I also get when running on master without my changes.

Reviewers: liyintang

Reviewed By: liyintang

CC: gauravm, hbase-eng@

Differential Revision: https://phabricator.fb.com/D906162

Task ID: 2566739

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1511427 13f79535-47bb-0310-9956-ffa450edef68