Make node to be the slave of a master.

def replicate(ctx, args):
    """Make node to be the slave of a master.
    """
    slave = ClusterNode.from_uri(args.node)
    master = ClusterNode.from_uri(args.master)
    if not master.is_master():
        ctx.abort("Node {!r} is not a master.".format(args.master))

    try:
        slave.replicate(master.name)
    except redis.ResponseError as e:
        ctx.abort(str(e))

    Cluster.from_node(master).wait()