Adding a service sometimes fails with UnknownError as the error code

When trying to add a service on *nix platforms, QServiceManger::addService() sometimes fails with an UnknownError error code.

The problem is that the ids generated for the services use QUUid::createUuid() which in turn uses the rand() function to generate the uuids. However the rand()unction isn't being seeded properly which results in it being used to generate ids which have already been used.