tests/functional/dummy.py: addAddr IPv6 support

IPv6 address support added to dummy's addAddr function.

Change-Id: I683971578ef7bb4a25f65d61d939e96bc976d32e
Signed-off-by: Petr Horáček <phoracek@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32614
Reviewed-by: Dan Kenigsberg <danken@redhat.com>