Run permission target switch action only for visible widgets

Permission details page was incorrectly evaluated as dirty (update button enabled) right after load when permission type={subtree,filter} and some attrs are set.

Can be reproduced by opening 'Modify Automount maps' permission.

The culprit is that attrs widget is populated and dirty-checked even targets where it doesn't belong.

Fixed by running target_mapping action only for visible targets.

https://fedorahosted.org/freeipa/ticket/3527