Print warning for misconfigured contract-first endpoints

When user provides misconfigured contract-first endpoints as below, the stack silently ignore the request of using the specified contract and generates the wsdl (code-first).

@Stateless
@WebService(portName = "SimpleEchoPort",wsdlLocation = "META-INF/wsdl/Echo.wsdl")
public class SimpleEcho {
...
}

(notice there's no serviceName specified, hence the stack won't know which port/service to use from the contract)

We should likely print a warning in this scenario, asking the user if he really wants a contract-first endpoint.