OS-438, IPv6 support for Infoblox

* In https://jira.inca.infoblox.com:8443/browse/OPENSTACK-438 you may grab shell script to test functionality.
* Currently we support only DUID-LL stateful IPv6 (https://tools.ietf.org/html/rfc3315#section-9.4), so to get IPv6 in stateful mode run dhclient -6 -D LL eth0

Still dont get it. I calculate it. There is 16 spaces. And yes - it's part of "for" loop.

```
        try:
            for relay_ip in relay_ips:
                netaddr.IPAddress(relay_ip)
        except...
```