ui: split setup of VNC auth scheme into separate method The vnc_display_open method is quite long and complex, so move the VNC auth scheme decision logic into a separate method for clarity. Also update the comment to better describe what we are trying to achieve. Signed-off-by: Daniel P. Berrange <berrange@redhat.com> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>