Prompt credentials for installing/deleting sounds

Actually we probably want to confirm credentials in all locked cases
not just when starting the user -- fewer corners to special case.

Fix: 34734809
Test: manual. set a work profile lock, screen off/on, open sound settings, try to set a work ringtone. first attempt should prompt for credentials, second attempt should not until next screen-off.
Change-Id: I1fea94f3b0d1b768b22741b887d9891f5e318549