qgen: improve DML statement comparison validation

The random query generator needs to have its DML correctness algorithm improved. It's not simply enough to count the rows, or even compare all the rows: there's no guarantee a conflicted INSERTed or UPSERTed row in one database will match that in the other database, though the primary keys should always match. In cases where the primary key matches but the rows of the other columns differ, we have to have known if the values in the other columns were part of a set of rows attempted to be inserted/upserted.