RowSetTree: do not allow intiialized RowSetTree objects to be reused.
RowSetTree: do not allow intiialized RowSetTree objects to be reused.

Change-Id: Iaca91b904978b8c9ab7581a16c2917c73bc40a3d
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2248
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>
Tested-by: jenkins

InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,helifu/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,InspurUSA/kudu,andrwng/kudu,InspurUSA/kudu,helifu/kudu,cloudera/kudu,EvilMcJerkface/kudu,helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,andrwng/kudu,andrwng/kudu,EvilMcJerkface/kudu,cloudera/kudu,helifu/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,andrwng/kudu,cloudera/kudu,helifu/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,EvilMcJerkface/kudu