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>

ipatests/test_ipaserver/test_install/test_installer.py

@@ -5,7 +5,7 @@ from __future__ import absolute_import
 
 import six
 
-from abc import ABCMeta, abstractproperty
+from abc import ABCMeta, abstractmethod
 from collections import namedtuple
 import itertools
 
@@ -21,7 +21,8 @@ class InstallerTestBase(six.with_metaclass(ABCMeta, object)):
     OPTS_DICT = {}
 
     # don't allow creating classes with tested_cls unspecified
-    @abstractproperty
+    @property
+    @abstractmethod
     def tested_cls(self):
         return None