Skip ipv6 tests on system without ipv6 support

On system without ipv6 support, CONFIG_IPV6 disabled kernel for
instance, WSGI service testcases for ipv6 would fail for "[Errno 97]
Address family not supported by protocol".

Since there is no easy way to detect actual ipv6 support,
socket.has_ipv6 not working for this case, simply skip ipv6 tests if
errno.EAFNOSUPPORT happens.

Fixes: bug 1174404

Change-Id: I9fa8653f5ccfbcb8c31c51bfda137cb58388afde
Merge "Skip ipv6 tests on system without ipv6 support"