Add an option to proxy namerd configuration to use NODE_NAME as url config

[FuzzOli87]

I setup linkerd-tcp to run on my cluster alongside Linkerd in a CNI configuration as a Daemonset. In my Kubernetes version 1.5.1, using hostNetwork: true doesn't give access to Kubernete's DNS options(for example, namerd.default.svc.cluster.local) A solution to this would be to expose the web port from Namerd as a NodePort service, however, this would require using the downward API env variable "NODE_NAME" to be able to access the Namerd NodePort service. The problem is that the downward API isn't available for ConfigMap resources.

A workaround was to hardcode a LoadBalancer service URL as the namerd url config for Linkerd-TCP.

I think that a configuration option to allow the url to be built from "NODE_NAME" env variable would solve this more elegantly as a solution to running Linkerd-TCP as a DaemonSet with CNI. Maybe a "fromNodePort" or something.

Of course, this might not be needed with Kubernetes 1.6 because they added a "ClusterFirstWithHostNet" dnsPolicy option which keeps DNS settings even with hostNetwork: true. I haven't updated yet so I haven't played with that option.

[adrianchifor]

@FuzzOli87 do you have an example of the k8s artifact or configuration on how you got linkerd-tcp setup alongside linkerd in a CNI config DaemonSet? I can't seem to find any examples. Would greatly appreciate it.