ipapython/admintool.py: use SERVER_NOT_CONFIGURED
    
    Commit 9182917280a5c2590fa677729db54b38a9ac4d1f introduced
    SUCCESS, SERVER_INSTALL_ERROR and SERVER_NOT_CONFIGURED to
    deal with cases when server is not configured.
    Actually use SERVER_NOT_CONFIGURED in log_failure instead of 2.
    
    Related-to: https://pagure.io/freeipa/issue/6843
    Signed-off-by: François Cami <fcami@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>