Make etcd data dir configurable.

Closes: #1073
Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

roles/etcd/templates/etcd-docker.service.j2

@@ -13,7 +13,7 @@ ExecStart={{ docker_bin_dir }}/docker run --restart=on-failure:5 \
 --net=host \
 -v /etc/ssl/certs:/etc/ssl/certs:ro \
 -v {{ etcd_cert_dir }}:{{ etcd_cert_dir }}:ro \
--v /var/lib/etcd:/var/lib/etcd:rw \
+-v {{ etcd_data_dir }}:/var/lib/etcd:rw \
 {% if etcd_memory_limit is defined %}
 --memory={{ etcd_memory_limit|regex_replace('Mi', 'M') }} \
 {% endif %}