[HBASE-8185] Make the use of client side scan in map reduce configurable.

Author: manukranthk

Summary: This diff tries to make the client side scan feature configurable in the mapreduce and mapred.

Test Plan: Not yet decided.

Reviewers: adela, rshroff

Reviewed By: adela

CC: hbase-eng@

Differential Revision: https://phabricator.fb.com/D946368

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1518314 13f79535-47bb-0310-9956-ffa450edef68