Do not shake the padlock until there's an error

We were previously shaking it for help messages, that don't
interrupt scanning.
We should only animate the padlock for hard errors.

Fixes: 139838611
Test: try face auth outside of field of view
Test: try face auth outside with face occluded
Change-Id: I699befc0e748fcc057decfda1c8fc58469695ad8