Add optional deployment mode for Docker etcd_deployment_type

Running etcd in Docker reduces the number of individual file
downloads and services running on the host.

Note: etcd container v3.0.1 moves bindir to /usr/local/bin

Fixes: #298

roles/etcd/tasks/install.yml

@@ -1,9 +1,38 @@
 ---
-- name: Install | Copy etcd binary
+- name: Install | Copy etcd binary from downloaddir
   command: rsync -piu "{{ etcd_bin_dir }}/etcd" "{{ bin_dir }}/etcd"
+  when: etcd_deployment_type == "host"
   register: etcd_copy
+
+- name: Install | Copy etcdctl binary from downloaddir
+  command: rsync -piu "{{ etcd_bin_dir }}/etcdctl" "{{ bin_dir }}/etcdctl"
+  when: etcd_deployment_type == "host"
   changed_when: false
 
-- name: Install | Copy etcdctl binary
-  command: rsync -piu "{{ etcd_bin_dir }}/etcdctl" "{{ bin_dir }}/etcdctl"
+#Plan A: no docker-py deps
+- name: Install | Copy etcdctl binary from container
+  command: sh -c "/usr/bin/docker rm -f etcdctl-binarycopy;
+           /usr/bin/docker create --name etcdctl-binarycopy {{ etcd_image_repo }}:{{ etcd_image_tag }} &&
+           /usr/bin/docker cp etcdctl-binarycopy:{{ etcd_container_bin_dir }}etcdctl {{ bin_dir }}/etcdctl &&
+           /usr/bin/docker rm -f etcdctl-binarycopy"
+  when: etcd_deployment_type == "docker"
   changed_when: false
+
+#Plan B: looks nicer, but requires docker-py on all hosts:
+#- name: Install | Set up etcd-binarycopy container
+#  docker:
+#    name: etcd-binarycopy
+#    state: present
+#    image: "{{ etcd_image_repo }}:{{ etcd_image_tag }}"
+#  when: etcd_deployment_type == "docker"
+#
+#- name: Install | Copy etcdctl from etcd-binarycopy container
+#  command: /usr/bin/docker cp "etcd-binarycopy:{{ etcd_container_bin_dir }}etcdctl" "{{ bin_dir }}/etcdctl"
+#  when: etcd_deployment_type == "docker"
+#
+#- name: Install | Clean up etcd-binarycopy container
+#  docker:
+#    name: etcd-binarycopy
+#    state: absent
+#    image: "{{ etcd_image_repo }}:{{ etcd_image_tag }}"
+#  when: etcd_deployment_type == "docker"