Fix etcd install with docker and etcd_kubeadm_enabled (#5777)

- This solves issue #5721 & #5713 (dupes)
  - Provide a cleaner default usage pattern for the download role
    around etcd that supports 'host' and 'docker' properly
  - Extract the 'etcdctl' as a separate task install piece and reuse it where
    appropriate
  - Update the kubeadm-etcd task to reflect the above change

roles/kubernetes/master/tasks/kubeadm-etcd.yml

@@ -16,3 +16,12 @@
   include_tasks: "{{ role_path }}/../../etcd/tasks/install_host.yml"
   vars:
     etcd_cluster_setup: true
+  when: etcd_deployment_type == "host"
+
+- name: Ensure etcdctl binary is installed
+  include_tasks: "{{ role_path }}/../../etcd/tasks/install_etcdctl_docker.yml"
+  vars:
+    etcd_cluster_setup: true
+    etcd_retries: 4
+  when:
+    - etcd_deployment_type == "docker"