Fix 6101396: Added password check when turning biometric weak liveliness off

Forcing the user to confirm their password when they turn liveliness off to
prevent a someone else besides the owner from turning it off.

Also renamed CONFIRM_EXISTING_FOR_BIOMETRIC_IMPROVE_REQUEST to
CONFIRM_EXISTING_FOR_BIOMETRIC_WEAK_IMPROVE_REQUEST.

Change-Id: I4244c9a16340839b7cb7b4a1f9ca395db0c30eee