Mark two failing automember tests as xfail

Two automember tests of the XML-RPC test suite have started to fail with
389-DS 1.4.0.21 update. The test failure seems to be related to a change of
389-DS' automember plugin,
https://www.port389.org/docs/389ds/design/automember-postop-modify-design.html.

See: https://pagure.io/freeipa/issue/7855
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipatests/test_xmlrpc/test_automember_plugin.py

@@ -257,6 +257,7 @@ class TestAutomemberRebuildHostMembership(XMLRPC_test):
         )
         hostgroup1.retrieve()
 
+    @pytest.mark.xfail(reason='freeipa ticket 7855', strict=True)
     def test_rebuild_membership_hostgroups(self, automember_hostgroup,
                                            hostgroup1, host1):
         """ Rebuild automember membership for hosts, both synchonously and
@@ -307,6 +308,7 @@ class TestAutomemberRebuildGroupMembership(XMLRPC_test):
         )
         group1.retrieve()
 
+    @pytest.mark.xfail(reason='freeipa ticket 7855', strict=True)
     def test_rebuild_membership_groups(self, automember_group, group1, user1):
         """ Rebuild automember membership for groups, both synchonously and
         asynchronously. Check the user has been added to the group. """