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/set_facts.yml

@@ -14,3 +14,7 @@
       {% endfor %}
 - set_fact:
     is_etcd_master: "{{ inventory_hostname in groups['etcd'] }}"
+- set_fact:
+    etcd_after_v3: etcd_version | version_compare("v3.0.0", ">=")
+- set_fact:
+    etcd_container_bin_dir: "{% if etcd_after_v3 %}/usr/local/bin/{% else %}/{% endif %}"