libcacard: introduce new vcard_emul_logout

vcard_emul_reset currently only logs NSS out, but there is a TODO
for potentially sending insertion/removal events when powering down
or powering up.

For clarity, this commit moves the current guts of vcard_emul_reset to
a new vcard_emul_logout function which will never send insertion/removal
events. The vcard_emul_reset function now just calls vcard_emul_logout,
but also retains its TODO for watching power state transitions and sending
insertion/removal events.

Signed-off-by: Ray Strode <rstrode@redhat.com>
Reviewed-By: Robert Relyea <rrelyea@redhat.com>
Reviewed-By: Alon Levy <alevy@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>