[HBASE-9815] Provide a batch API to retrieve Histograms for a list of regions in a regionserver.

Author: manukranthk

Summary: This diff attempts to add a HRegionServer API which gets a list of histograms for the given list of regions.

Test Plan: Modified the unit test TestHFileHistogramE2E to add checks to compare the return from the batch function with the previous one.

Reviewers: liyintang, aaiyer

Reviewed By: liyintang

CC: hbase-eng@, andrewcox

Differential Revision: https://phabricator.fb.com/D1256318

Task ID: 3875260

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1584857 13f79535-47bb-0310-9956-ffa450edef68
[HBASE-9930] Add back the metascan functions which take byte[] as input.

Author: manukranthk

Summary: This diff adds metascan functions in MetaScanner which are similar to the original functions.

Test Plan: Simple change.

Reviewers: daviddeng

Reviewed By: daviddeng

CC: hbase-eng@

Differential Revision: https://phabricator.fb.com/D1258271

Task ID: 3540638

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.89-fb@1584858 13f79535-47bb-0310-9956-ffa450edef68