pylint: Fix deprecated-decorator
    
    Pylint 2.9 introduced new checker:
    > The decorator is marked as deprecated and will be removed in the
      future.
    
    - @abstractproperty has been deprecated since Python3.3 [0]
    - @abstractclassmethod has been deprecated since Python3.3 [1]
    
    [0]: https://docs.python.org/3/library/abc.html#abc.abstractproperty
    [1]: https://docs.python.org/3/library/abc.html#abc.abstractclassmethod
    
    Fixes: https://pagure.io/freeipa/issue/9117
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>