[core worker] Python core worker object interface (#5272)

python/ray/node.py

@@ -230,6 +230,12 @@ class Node(object):
         """Get the node's plasma store socket name."""
         return self._plasma_store_socket_name
 
+    @property
+    def unique_id(self):
+        """Get a unique identifier for this node."""
+        return "{}:{}".format(self.node_ip_address,
+                              self._plasma_store_socket_name)
+
     @property
     def webui_url(self):
         """Get the cluster's web UI url."""