Implement possibility to work against ZooKeeper

This implementation is using the same interface (AbstractDCS) as Etcd
class. It means that there should be no problem to implement another
plugin to work agains Consul for example.

postgres0.yml

@@ -1,12 +1,18 @@
-loop_wait: 10
+ttl: &ttl 30
+loop_wait: &loop_wait 10
 restapi:
   listen: 127.0.0.1:8008
   connect_address: 127.0.0.1:8008
 etcd:
   scope: batman
-  ttl: 30
+  ttl: *ttl
   host: 127.0.0.1:4001
   #discovery_srv: my-etcd.domain
+#zookeeper:
+#  scope: batman
+#  session_timeout: *ttl
+#  reconnect_timeout: *loop_wait
+#  hosts: 127.0.0.1:2181
 postgresql:
   name: postgresql0
   listen: 127.0.0.1:5432