'Extend a cluster with nodes provisioned via libcloud.'

def extend_cluster(self, reactor, cluster, count, tag, starting_index):

    names = []
    for index in range(starting_index, (starting_index + count)):
        names.append(self._make_node_name(tag, index))
    results = self._create_nodes(reactor, names)
    def add_node(node, index):
        return self._add_node_to_cluster(reactor, cluster, node, index)
    for (i, d) in enumerate(results):
        d.addCallback(add_node, (starting_index + i))
    return results
