func (c *cluster) Leader(timeout time.Duration) *raftNode {
	start := time.Now()
	for true {
		for _, n := range c.nodes {
			if n.raft.State() == raft.Leader {
				return n
			}
		}
		if time.Now().Sub(start) > timeout {
			return nil
		}
		time.Sleep(time.Millisecond)
	}
	return nil
}
func (c *cluster) Leader(timeout time.Duration) *raftNode {
	start := time.Now()
	for true {
		for _, n := range c.nodes {
			if n.raft.State() == raft.Leader {
				return n
			}
		}
		if time.Now().Sub(start) > timeout {
			return nil
		}
		time.Sleep(time.Millisecond)
	}
	return nil
}
// Leader returns the node that is currently the Leader, if there is no
// leader this function blocks until a leader is elected (or a timeout occurs)