Make specifying zookeeper in topo files optional

For pure golang topologies we don't require zookeeper anymore,
so we should also not require zookeeper to be specified in the topo file.

python/topology/config.py

@@ -121,9 +121,6 @@ def _read_defaults(self, network):
             priv_net = DEFAULT_PRIV_NETWORK
         self.subnet_gen = SubnetGenerator(def_network, self.args.docker, self.args.in_docker)
         self.prvnet_gen = SubnetGenerator(priv_net, self.args.docker, self.args.in_docker)
-        if "zookeepers" not in defaults:
-            logging.critical("No zookeeper configured in the topology!")
-            sys.exit(1)
         self.default_mtu = defaults.get("mtu", DEFAULT_MTU)
 
     def generate_all(self):

python/topology/topo.py

@@ -329,10 +329,15 @@ def _gen_sig_entries(self, topo_id):
         self.topo_dicts[topo_id]['SIG'][elem_id] = d
 
     def _gen_zk_entries(self, topo_id, as_conf):
+        if ("defaults" not in self.args.topo_config_dict or
+            "zookeepers" not in self.args.topo_config_dict["defaults"]):
+            return
         zk_conf = self.args.topo_config_dict["defaults"]["zookeepers"]
         if len(zk_conf) > 1:
             logging.critical("Only one zk instance is supported!")
             sys.exit(1)
+        if len(zk_conf) < 1:
+            return
         addr = zk_conf[1].get("addr", None)
         port = zk_conf[1].get("port", None)
         zk_entry = self._gen_zk_entry(addr, port, self.args.in_docker, self.args.docker)

topology/Tiny.topo

@@ -1,8 +1,4 @@
 --- # Tiny Topology
-defaults:
-  zookeepers:
-    1:
-      addr: 127.0.0.1
 ASes:
   "1-ff00:0:110": # old 1-11
     core: true