Tests that are agnostic about the IP protocol used will use whichever
the socket_helper module deems appropriate for the host.

there's a _lot_ more cleanup that could be done in here.
the capability skip decorators are applied in an inconsistent
manner.  some on the base class, others way down on the leaf
Test classes.  yuck.

Also makes the test_multiprocessing suites work on IPv6-only hosts.