Ticket #48748 - Fix memory_leaks test suite teardown failure

Bug Description: TearDown part of memory_leaks/range_search_test.py
goes with error. Because of that valgrind_disable(sbin_dir) is
never executed. It causes all next setup-ds.pl commands fail.

Fix Description: Change topology.standalone object to just standalone.
Otherwise, it is not found.

https://fedorahosted.org/389/ticket/48748

Reviewed by: mreynolds (Thanks!)

dirsrvtests/suites/memory_leaks/range_search_test.py

@@ -55,8 +55,8 @@ def topology(request):
     standalone.clearTmpDir(__file__)
 
     def fin():
-        topology.standalone.delete()
-        sbin_dir = get_sbin_dir(prefix=topology.standalone.prefix)
+        standalone.delete()
+        sbin_dir = get_sbin_dir(prefix=standalone.prefix)
         valgrind_disable(sbin_dir)
     request.addfinalizer(fin)