SSSD info plugin is immutable if not preconfigured
    
    The SSSD info plugin configures SSSD and modules in
    Apache as root during installation. This cannot be
    done in the UI so we must not allow users to modify
    the state if it was not "preconfigured" during
    install.
    
    If it has been configured then users are allowed
    to enable/disable the plugin.
    
    This is controlled by a value stored in the
    info_config table, preconfigured.
    
    The plugin configuration is hidden from the UI by
    overridding the get_config_object() method.
    
    https://fedorahosted.org/ipsilon/ticket/111
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    Reviewed-by: Rob Crittenden <rcritten@redhat.com>