Add a node to cluster.

        :param node: should be formated like this
        `{"addr": "", "role": "slave", "master": "master_node_id"}

def add_node(self, node):
        """Add a node to cluster.

        :param node: should be formated like this
        `{"addr": "", "role": "slave", "master": "master_node_id"}
        """
        new = ClusterNode.from_uri(node["addr"])
        cluster_member = self.nodes[0]
        check_new_nodes([new], [cluster_member])

        new.meet(cluster_member.host, cluster_member.port)
        self.nodes.append(new)

        self.wait()

        if node["role"] != "slave":
            return

        if "master" in node:
            target = self.get_node(node["master"])
            if not target:
                raise NodeNotFound(node["master"])
        else:
            masters = sorted(self.masters, key=lambda x: len(x.slaves(x.name)))
            target = masters[0]

        new.replicate(target.name)
        new.flush_cache()
        target.flush_cache()