Update documentation to recommend headless Service instead of vanilla ClusterIP

[f5yacobucci]

Update documentation to recommend headless Service instead of vanilla ClusterIP

// Do not include requests for development or report issues with code or products here.
This repository contains documentation only.

Bugs

Describe the bug in detail:

• What doc are you reporting an issue with (provide URL)?
  http://clouddocs.f5.com/containers/v2/kubernetes/kctlr-modes.html

• What information is inaccurate?

• Is information missing?
  When discussing cluster mode we don't discuss Service type, we do discuss Service type in the NodePort discussion. This point is obvious in that to support NodePort the Service must be in NodePort. We should discuss using headless Services in cluster mode. When using headless Services the Service will not receive a ClusterIP nor will kubeproxy create iptables rules for traffic. The assumption being that if this Service should be a point of ingress, and that traffic will be handled via the BIG-IP, then the user probably doesn't want traffic from other sources - via kubeproxy and the ClusterIP, or even worse possibly via an exposed NodePort.

Add information about headless Services including the reasoning above.

• Is a code sample incorrect?

Requests

Provide details regarding what you would like to see added to our documentation:

Environment

• Cloud Foundry
• Kubernetes
• OpenShift
• Mesos/Marathon)

Use Case

(i.e., what are you trying to do that you can't find documentation for?)