TOMEE-2753 Bean validation on response with no response entity failing

[Jonathan Gallimore]

So this one was a bit weird. A basic service like this:

        @GET
        @Path("simple")
        public void service() {
            // no-op; should return a 204 no content
            System.out.println("Service invoked");
        }

Was failing, as bean validation was kicking in for the response, and
failing because the response doesn't have an entity.

I've tweaked the OutInterceptor added in CxfRsHttpListener to behave a
little more like org.apache.bval.cdi.BValInterceptor#invoke, in that it
checks for any constraints set on the response type.

PR is here: https://github.com/apache/tomee/pull/622

I'll merge it in tomorrow, and run the JAX-RS TCK tests against it.
Certainly some are failing because of this issue, so I'm expecting more to
pass with the fix.

Feedback is welcome.

Jon