Reduce heartbeat frequency to 500ms to reduce etcd cpu load

Per https://github.com/coreos/etcd/pull/3097 reduce heartbeat
to 500ms until we can ensure etcd 2.1 is in use

Reduces the impact of but doesn't fix BZ1250310

roles/etcd/templates/etcd.conf.j2

@@ -16,8 +16,8 @@ ETCD_NAME=default
 {% endif %}
 ETCD_DATA_DIR={{ etcd_data_dir }}
 #ETCD_SNAPSHOT_COUNTER="10000"
-#ETCD_HEARTBEAT_INTERVAL="100"
-#ETCD_ELECTION_TIMEOUT="1000"
+ETCD_HEARTBEAT_INTERVAL="500"
+ETCD_ELECTION_TIMEOUT="2500"
 ETCD_LISTEN_CLIENT_URLS={{ etcd_listen_client_urls }}
 #ETCD_MAX_SNAPSHOTS="5"
 #ETCD_MAX_WALS="5"