Make etcd data dir configurable.

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

roles/etcd/templates/etcd.j2

@@ -1,4 +1,4 @@
-ETCD_DATA_DIR=/var/lib/etcd
+ETCD_DATA_DIR={{ etcd_data_dir }}
 ETCD_ADVERTISE_CLIENT_URLS={{ etcd_client_url }}
 ETCD_INITIAL_ADVERTISE_PEER_URLS={{ etcd_peer_url }}
 ETCD_INITIAL_CLUSTER_STATE={% if etcd_cluster_is_healthy.rc != 0 | bool %}new{% else %}existing{% endif %}