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

I think we need to refactor exceptions module, because it keeps growing with no real purpose.

1. Generalize existing exceptions. For example, with current exception, we may replace multiple existing exceptions with InfobloxParseException(), and provide details inside the actual exception.
2. Remove unneeded exceptions
3. Replace exceptions in the calling code.

The comment seem unrelated to the actual problem we're solving with this commit, so the action item would be to create a Jira issue with this description. No need to implement it as part of this change.