Extend benchmark for ColumnarRowBlockToPB.
Extend benchmark for ColumnarRowBlockToPB.

Extend the origin ColumnarRowBlockToPB benchmark in two aspects.
Both column scale and selected row count are configurable.

Change-Id: Ie29937c316be624151e6c51e54545c4f023e603d
Reviewed-on: http://gerrit.cloudera.org:8080/13749
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@apache.org>
Tested-by: Kudu Jenkins

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu