uninstall: Don't fail on missing /var/lib/samba
    
    On some distros freeipa-server package may not depend on
    `/var/lib/samba` directory. In this case an uninstallation of
    ipaserver fails.
    
    Fixes: https://pagure.io/freeipa/issue/8461
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>