test_xmlrpc: fix TestAutomemberFindOrphans.test_find_orphan_automember_rules

Test scenario:
- create a hostgroup
- create a host
- create an automember rule for the hostgroup with a condition fulfilled
by the host
- delete the hostgroup
- call automember-rebuild (1)
- call automember-find-orphans to remove the orphan automember group
- call automember-rebuild(2)

The test was expecting the first rebuild command to fail but this
assumption is not true if the DS version is >= 1.4.0.22 because of the
fix for https://pagure.io/389-ds-base/issue/50077

Modify the test so that it expects failure only when DS is older.

Fixes: https://pagure.io/freeipa/issue/7902
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipatests/test_xmlrpc/test_automember_plugin.py

@@ -35,7 +35,9 @@ from ipaserver.plugins.automember import REBUILD_TASK_CONTAINER
 
 import time
 import pytest
+import re
 import unittest
+from pkg_resources import parse_version
 
 try:
     from ipaserver.plugins.ldap2 import ldap2
@@ -885,7 +887,6 @@ class TestAutomemberFindOrphans(XMLRPC_test):
 
         hostgroup1.retrieve()
 
-    @pytest.mark.skip(reason="Fails with 389-DS 1.4.0.22, see issue 7902")
     def test_find_orphan_automember_rules(self, hostgroup1):
         """ Remove hostgroup1, find and remove obsolete automember rules. """
         # Remove hostgroup1
@@ -893,12 +894,29 @@ class TestAutomemberFindOrphans(XMLRPC_test):
         hostgroup1.ensure_missing()
 
         # Test rebuild (is failing)
+        # rebuild fails if 389-ds is older than 1.4.0.22 where unmembering
+        # feature was implemented: https://pagure.io/389-ds-base/issue/50077
+        if not have_ldap2:
+            raise unittest.SkipTest('server plugin not available')
+        ldap = ldap2(api)
+        ldap.connect()
+        rootdse = ldap.get_entry(DN(''), ['vendorVersion'])
+        version = rootdse.single_value.get('vendorVersion')
+        # The format of vendorVersion is the following:
+        # 389-Directory/1.3.8.4 B2019.037.1535
+        # Extract everything between 389-Directory/ and ' B'
+        mo = re.search(r'389-Directory/(.*) B', version)
+        vendor_version = parse_version(mo.groups()[0])
+        expected_failure = vendor_version < parse_version('1.4.0.22')
+
         try:
             api.Command['automember_rebuild'](type=u'hostgroup')
         except errors.DatabaseError:
-            pass
+            rebuild_failure = True
         else:
-            pytest.fail("automember_rebuild was not failing with "
+            rebuild_failure = False
+        if expected_failure != rebuild_failure:
+            pytest.fail("unexpected result for automember_rebuild with "
                         "an orphan automember rule")
 
         # Find obsolete automember rules