Service Base Class And Service Insertion

In Havana and IceHouse, Neutron advanced services have made great progress. FWaaS, LBaaS, and VPNaas have been included in Neutron as experimental extensions. However the insertions of these services are accomplished either in implicit manner or on a virtual router. There isn't any well defined abstraction to express various service insertion mechanisms, such as L3, L2, or bump-in-the-wire. Furthermore, the three services are defined independently and lacks the hierarchical structure to maintain the common attributes of all services in a single object. Hence, the blueprint introduces the serviceBase object, from which all services inherits. The serviceBase object captures the common service properties and APIs to ensure the uniformity across all Neutron services.