Add logic in service_controller to skip create/update
if finalizer from a different controller is found.
The newly added finalizer will be checked by other controllers
implementing ILB services to determine if a given service is
already being managed by service_controller.
Moved finalizer check into cloudprovider code.
added unit test to verify new finalizer.
Modified existing unit test to create a fake service so that
attach/remove finalizer step can be tested.
