svc.configd should act consistently wrt service addition
If a service is added to /etc/svc/repository.db by anything
other than the system's svc.configd (say, by svccfg from a
pre-6178183 i.manifest), then svc.configd will fail
attempts to look up that service with "not found" and
attempts to add that service with "already exists".
If svc.configd can tell that the repository has been changed
externally, then it should either panic or reload the
database. Otherwise it should at least load the service
after returning "already exists" for an addition call.