Add ability for core plugin to implement advanced services

implements blueprint api-core-for-services

Add check for supported_extension_aliases in QuantumManager.
If core plugin supports certain service extension, then core plugin is
stored in service_plugins for the service type of this extension
so corresponding extension could set it as a controller for REST calls.

Change-Id: I9c883491f6f13770371e3444e7c17bd2164a7c07
Merge "Add ability for core plugin to implement advanced services"