httpinstance.disable_system_trust: Don't fail if module 'Root Certs' is not available
    
    Server installation failed when attmpting to disable module 'Root Certs' and
    the module was not available in HTTP_ALIAS_DIR. When the module is not
    available there's no need to disable it and the error may be treated as
    success.
    
    https://pagure.io/freeipa/issue/6803
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>