ctdb-tests: Skip some tests that don't work with IPv6

ctdb-tests: Skip some tests that don't work with IPv6

See the comments added to the tests.

It may be possible to rewrite these so they do something sane for
IPv6... some other time.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14227
RN: Fix IPv6 issues (NFS connection tracking, tests)

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Fri Jan  3 00:00:55 UTC 2020 on sn-devel-184

(backported from commit 9edf15afc219a1a782ec1e4d29909361bbabc744)

Signed-off-by: Martin Schwenke <martin@meltin.net>
Autobuild-User(v4-10-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-10-test): Tue Jan 14 12:46:17 UTC 2020 on sn-devel-144