As cited in
https://github.com/kubernetes/dns/issues/174 - this is documented to
work, and I don't see why it shouldn't work. We allowed the definition
of headless services without ports, but apparently nobody tested it very
well.
Manually tested clusterIP services with no ports - validation error.
Manually tested services with negative ports - validation error.
New tests failed, output inspected and verified. Now pass.
