IP reservation schema patch

[rinzler-17]

Addresses #30 (comment)

[rinzler-17]

Patch 12 keynotes:

1. Declared a parent schema called IPReservation which is extended by DefaultIPReservation (for regular equinix ip reservations) and VrfIPReservation (for vrf only ip reservations).
2. All 3 schemas for ip reservation are complete including all possible property fields cross referenced from API tests. additionalProperties was set to false in the child schema because of a bug in oas3.0 due to which the member field additionalProperties gets duplicated in child classes. This flagged runtime errors when instantiating class from Json response objects.
3. For responses containing the IPReservation schema-reference, JSON validation occurs during the parsing step based on the discriminator configuration specified in IPReservation. The subclass is decided by the required field type.
4. GET API responses for MetalGateway and VrfMetalGateway were basically the same with only vrf field being null in the former. Hence, VrfMetalGateway was removed from the spec and its usage was replaced by MetalGateway after adding a vrf property to the MetalGateway schema.

Note: 1, 2 and 3 overwrite some spec changes from patch 10.

[displague]

I've created an upstream patch for the added fields. I'm not upstreaming the base class changes at this time, it would not be conventional with the API spec so there is more to consider there.