Re-implemented IP policies with offset and length

[asadoughi]

• Implemented CRUD ip_policies plugin methods
• Implemented plugin ip_policy unit tests
• Added IP Policy logic to ipam.allocate_ip_address
• Implemented ip_policy ipam unit tests
• Implemented ip_policies extension
• Added ip_policies db models
• Implemented db_api ip_policy methods
• Implemented _make_ip_policy_dict view
• Fixed existing tests

An IP Policy is defined on a subnet or network definining what IPs to exclude from allocation. From a user perspective an IP Policy looks like the following:

{ "id": , "tenant_id": , "name": "foobar", "subnet_ids": [](list of uuids), "network_ids": [](list of uuids), "exclude": list of dictionaries (e.g. [{"offset": -1, "length": 3}]) }

"exclude" is always required. One of "subnet_ids" or "network_ids" is required. Only one policy is allowed per network.

A default policy is enabled on all subnets if no ip policies are specified on that subnet or its network. This default policy is established via JSON configuration as "default_ip_policy". The default for "default_ip_policy" is no policy.

[asadoughi]

Working on re-doing integration tests currently... do not merge yet, please. Thanks.

[asadoughi]

Integration tests complete with a few things fixed.

[jmeridth]

lgtm