Make ServiceDiscoveryManager.findService() consider all services
with the same matching feature announced.
Consider for example PubSub where usually the service itself announces
the PubSub feature as part of PEP, and where an additional PubSub
component exists. The old logic will just lookup the first matching
service with a PubSub feature announcement and check if for a matching
identiy. If we look for a real PubSub service, but stumble first over
user's service with PEP, then findService() will return 'null' although
there would have been a valid PubSub service.
