Improve ELB healthchecks for API

So after the presentation at the Deis office, we had some great feedback regarding making improvements to the AWS ELB healthchecks.

We have the API infrastructure in place in kops already to add health checks.. we just need some feedback from the community on what seems relevant here.

The biggest use case we heard about was pointing the ELB healhcheck to the `healthz` endpoint on the Kubernetes API server. Does anyone have anything else?

Review the existing API infrastructure in kops and how AWS ELB health checks are currently configured. Investigate whether the Kubernetes API server's healthz endpoint is suitable and gather the missing community requirements. Done means an agreed health-check endpoint and behavior, followed by an implementation and validation plan.

Written by the indexing model from the issue text.