Rework cluster/juju to reflect current work

This commit imports the latest development focus from the Charmer team
working to deliver Kubernetes charms with Juju.

Notable Changes:

- The charm is now assembled from layers in $JUJU_ROOT/layers
- Prior, the juju provider would compile and fat-pack the charms, this
  new approach delivers the entirety of Kubernetes via hyperkube.
- Adds Kubedns as part of `cluster/kube-up.sh` and verification
- Removes the hard-coded port 8080 for the Kubernetes Master
- Includes TLS validation
- Validates kubernetes config from leader charm
- Targets Juju 2.0 commands

cluster/kubectl.sh

@@ -116,7 +116,7 @@ kubectl="${KUBECTL_PATH:-${kubectl}}"
 
 if [[ "$KUBERNETES_PROVIDER" == "gke" ]]; then
   detect-project &> /dev/null
-elif [[ "$KUBERNETES_PROVIDER" == "ubuntu" || "$KUBERNETES_PROVIDER" == "juju" ]]; then
+elif [[ "$KUBERNETES_PROVIDER" == "ubuntu" ]]; then
   detect-master > /dev/null
   config=(
     "--server=http://${KUBE_MASTER_IP}:8080"