Make sure `collisionDetectGradTest` gets body idx.
Make sure `collisionDetectGradTest` gets body idx.

Otherwise it can't report which collision pair has bad gradients.

billhoffman/drake,manuelli/drake,manuelli/drake,billhoffman/drake,edowson/drake,thientu/drake,crogers3/drake,crogers3/drake,thientu/drake,edowson/drake,scottviteri/drake,edowson/drake,psiorx/drake,manuelli/drake,billhoffman/drake,tkoolen/drake,sheim/drake,astrorog/drake,astrorog/drake,tkoolen/drake,psiorx/drake,astrorog/drake,manuelli/drake,sheim/drake,tkoolen/drake,edowson/drake,edowson/drake,hanssusilo/drake,manuelli/drake,edowson/drake,sheim/drake,hanssusilo/drake,tkoolen/drake,astrorog/drake,crogers3/drake,scottviteri/drake,sheim/drake,edowson/drake,sheim/drake,tkoolen/drake,scottviteri/drake,billhoffman/drake,billhoffman/drake,scottviteri/drake,psiorx/drake,manuelli/drake,psiorx/drake,hanssusilo/drake,tkoolen/drake,hanssusilo/drake,scottviteri/drake,sheim/drake,crogers3/drake,psiorx/drake,sheim/drake,thientu/drake,edowson/drake,psiorx/drake,hanssusilo/drake,manuelli/drake,hanssusilo/drake,hanssusilo/drake,scottviteri/drake,billhoffman/drake,crogers3/drake,billhoffman/drake,astrorog/drake,thientu/drake,hanssusilo/drake,psiorx/drake,thientu/drake,thientu/drake,crogers3/drake,billhoffman/drake,tkoolen/drake,astrorog/drake,thientu/drake,astrorog/drake,crogers3/drake,crogers3/drake,psiorx/drake,scottviteri/drake,sheim/drake