VPC API support

A subset of AWS VPC resources are supported in either directly via Contrail-API or via Neutron-API through route-table extension. Design details are present in this blueprint.

Some of these resources can be used on their own even without VPC-API. For e.g. the external_gateway (in NAT mode) functionality on a Neutron router is implemented by

• creating a service-instance that does NAT in a netns
• creating a route-table in the project if it doesn't exist
• creating a 0.0.0.0/0 route with the service-instance as nexthop and add it to route-table
• associate this route-table to all virtual-networks connected to the logical-router

Examples of using Neutron-API to manipulate these new resources can be traced from here.