Copy kubectl from docker container

Nearly the last stage of source all components to containers.
Kubectl will be called from hyperkube image.

Remaining tasks:
 * Move kube_version variable to kubernetes/preinstall
 * Drop placeholder download.nothing requirement

roles/download/defaults/main.yml

@@ -15,8 +15,6 @@ calico_cni_version: v1.3.1
 weave_version: v1.5.0
 
 # Download URL's
-kubectl_download_url: "https://storage.googleapis.com/kargo/{{kube_version}}_kubernetes-kubectl"
-
 etcd_download_url: "https://storage.googleapis.com/kargo/{{etcd_version}}_etcd"
 calico_cni_download_url: "https://storage.googleapis.com/kargo/{{calico_cni_version}}_calico-cni-plugin"
 calico_cni_ipam_download_url: "https://storage.googleapis.com/kargo/{{calico_cni_version}}_calico-cni-plugin-ipam"
@@ -62,14 +60,6 @@ downloads:
     unarchive: true
     owner: "etcd"
     mode: "0755"
-  kubernetes_kubectl:
-    dest: kubernetes/bin/kubectl
-    version: "{{kube_version}}"
-    sha256: "{{vars['kube_checksum'][kube_version]['kubectl']}}"
-    source_url: "{{ kubectl_download_url }}"
-    url: "{{ kubectl_download_url }}"
-    owner: "kube"
-    mode: "0755"
   nothing:
     enabled: false