test_topology_plugin: Don't rely on order of an attribute's values
Order of Python dicts/sets was always unreliable, but in Python 3
it's usually different every time. This affects the order in which
values of a LDAP attribute appear.
LDAP values are also specified to be unordered.
Part of the work for: https://fedorahosted.org/freeipa/ticket/4985
Reviewed-By: Martin Basti <email@example.com>