[89-fb] [HBASE-7509] Regionserver support to control quorum reads

Author: aaiyer

Summary:
It will be good to have the ability to control the
paramaters for quorum reads while the regionserver is still running.

We want to control:
  1) the timeout that we wait for, before initiating the second read.
  2) number of threads allocated for quorum reads
     - setting this to 0 will disable quorum reads

 Depends on the quorum diff in HDFS to add the DFSClient calls.
https://phabricator.fb.com/D615354

 Will not commit this until alligator is updated. But, putting out
 for review together.

 Notes for Amit: (Will not be part of the commit)
         b398400e7b11 remove src/main/java/org/apache/hadoop/hbase/client/ParallelHDFSReads.java
         0ecb342447e2 lint errors
         4e609ef08613 add a ruby script to manage quorum reads
         d3e5cb243c06 control timeout as well
         20bd6254ad8a revert HMasterInterface
         7378e5e30541 rename function in setNumQuorumReadThreadsForHDFS -> setNumHDFSQuorumReadThreads
         cf443b6c65f7 regionserver support

Test Plan: deploy to dev cluster and set the params on the fly

Reviewers: liyintang, kannan, kranganathan

Reviewed By: liyintang

CC: hbase-eng@, sdong, hkuang, hdfs-dev@

Differential Revision: https://phabricator.fb.com/D635914

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1429973 13f79535-47bb-0310-9956-ffa450edef68