Need improved/HTTPS-centric GKE Ingress + ESP + gRPC example

I had a tough time figuring out how to get an Ingress on GKE to behave with ESP, with HTTPS end-to-end. I believe the underlying issues have to do with health checks and readiness probes and how ingress-gke handles those. I commented on the following issue in that project: https://github.com/kubernetes/ingress-gce/issues/18#issuecomment-418262864

Once health checks can be customized, perhaps an update can be made to [esp_echo_gke_ingress.yaml](https://github.com/GoogleCloudPlatform/endpoints-samples/blob/master/k8s/esp_echo_gke_ingress.yaml).