Move service abstract base class check to launchers

[Elena Ezhova]

The following check [1] is supposed to verify that a service that is being launched is an instance of service.ServiceBase abstract base class. However in some projects services are launched by instantiating a launcher (ServiceLauncher or ProcessLauncher) and then directly calling its launch_service method [2]. In this case the check [1] never executes.

That's why it has to be moved to launch_service methods of the both launcher classes.

[1] https://github.com/openstack/oslo.service/blob/master/oslo_service/service.py#L624-L626
[2] https://github.com/openstack/neutron/blob/master/neutron/wsgi.py#L251-L252

[Elena Ezhova (eezhova)]

Related review: https://review.openstack.org/#/c/194143/