[HBASE-11187] Limit the number of client threads per regionserver

Author: elliott

Summary:
When there are lots of HTables created and a region server becomes slow
to respond this will create lots of threads in the HConnection(TableServers).

This patch adds a config that will limit the number of thread per regionserver
that the HBase client can spawn. Above that number the requests will fail fast.

Test Plan: verynicetests

Reviewers: aaiyer, rshroff

Reviewed By: rshroff

Subscribers: hbase-eng@

Differential Revision: https://phabricator.fb.com/D1331985

Tasks: 4330194

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1595280 13f79535-47bb-0310-9956-ffa450edef68
[0.89-fb] [master] Move should not immediately clean up META.

Author: aaiyer

Summary:
Cleaning up META will be done automatically, after the original Region owner
closes the region.

Cleaning META immediately can allow the meta scanner to
reassign the region, before it is completely closed on the original owner.
We should be avoiding that.

Test Plan: run on shadow

Reviewers: rshroff, manukranthk

Reviewed By: manukranthk

Subscribers: hbase-eng@

Differential Revision: https://phabricator.fb.com/D1333381

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1595281 13f79535-47bb-0310-9956-ffa450edef68