Description of problem:
The "users" area of settings allows fingerprint data to be set/cleared without authentication

Version-Release number of selected component (if applicable):
control-center-3.14.2-2.fc21.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Walk up to someone's session
2. Open Settings->Users
3. Set your fingerprint to log in

Actual results:
Anyone can override existing fingerprint login with their own

Expected results:
It should require the "users" panel to be unlocked before manipulating fingerprint settings.

Additional info:
Looks like this was previously reported as #827968 but was closed unfixed.