I don't think you can "go for a scrum penalty". If you dominate the scrum and the other guys collapse the scrum you get a penalty. It's not up to you to dominate or to collapse the scrum but technically it's caused by the other team.
You also can't half dominate the scrum. If the scrum is even, you risk collapsing it conceding a penalty. Might as well push as hard as you can and see what happens. Though I am told the tighthead prop [and sometimes the loosie also] has semi legal (could well be illegal) tricks on how to make the other guy cry and collapse.
Well they did. The commentator said lets go for a scrum penalty, (as it was in easy kicking range)and they got it. Also mentioned to the Lions I think later on. Ive seen and heard that before in a game, so they must do something to try to force a scrum collapse.