Fixes tenant_id

See https://github.com/rackerlabs/quark/pull/35
Merge pull request #43 from rackerlabs/ganked_fix_tenant

Fixes tenant_id
RM3889

- change IPPolicy to use CIDRs for exclusion
- no longer allow offset/lengths
- changed IPPolicyRule to IPPolicyCIDR
- default CIDRs excluded are network ip and broadcast ip, these are detected and added in the IPPolicy model.
- no longer allow configurable default policies becase we can't detect if subnet is IPv4 or IPv6 at configuration time
- We are more strict about only allowing a user to provide either network_ids or subnet_ids.  We will throw an exception if they provide both.