HBASE-8306 Enhance TestJoinedScanners with ability to specify various parameters (Ted Yu)



git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1480277 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-YAHOO-312-trunk-gd