[HBASE-8500] Separates out the test case to make it more reliable

Author: rshroff

Summary:
The test was blacklisting a region server and then verifying whether
the regions were assigned to the blacklisted region servers or not.

Since, each individual test creates a new table, the number of regions were
too many, which might cause timeouts in some scenarios

Test Plan: MR and run the new test locally

Reviewers: manukranthk

Reviewed By: manukranthk

CC: hbase-eng@

Differential Revision: https://phabricator.fb.com/D847030

Blame Revision: ·

Task ID: 2479067

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1508569 13f79535-47bb-0310-9956-ffa450edef68