IIOP: make sure that handles serialization is being tested

IIOP client library implements Java EE2 handles API for EJB invocations over IIOP which are already tested in BasicIIOPInvocationTestCase in basic integration testsuite. One thing that which is missing in those tests is the serialization and deserialization of handle objects. The code of this operations is not trivial so it would be useful to make sure those are tested as well.