Otherwise the second attempt tot login after pressing "escape" key
on the login "freeze" and raise an exception about IOError operation
cancelled.
https://bugzilla.gnome.org/show_bug.cgi?id=681537
The fingerprint message is useful for users that click their
names in the user list to let them know if fingerprint login
is available.
This same place on screen (below the login entry) can potentially
be used for other messages as well.
This commit changes the variable and style names surrounding
this feature to be more generic.
A subsequent commit will leverage this functionality to provide
a hint on how to log in to the local enterprise domain controller
(if relevant).
https://bugzilla.gnome.org/show_bug.cgi?id=681975
GetUserVerifier can only be called from the greeter session,
and fails with AccessDenied in all other cases. Also, calling it
hides the real error from OpenReauthenticationChannel, which
instead should be logged.
https://bugzilla.gnome.org/show_bug.cgi?id=680750
