Added testing for IPv6 to peer grouper tests

So far the peer grouper only tests IPv4. As part of the IPv6 enabling the peer grouper testing now runs all tests for IPv6 too.
I can't help think that you might be better off defining an ipVersion type that's based on ``string``.  The IPv4 and IPv6 constants would be of this type, making them printable (which helps with my other suggestion).