func (c *cluster) LeaderPlus(n int) []*raftNode {
	r := make([]*raftNode, 0, n+1)
	ldr := c.Leader(time.Second)
	if ldr != nil {
		r = append(r, ldr)
	}
	if len(r) >= n {
		return r
	}
	for _, node := range c.nodes {
		if !containsNode(r, node) {
			r = append(r, node)
			if len(r) >= n {
				return r
			}
		}
	}
	return r
}
func (c *cluster) LeaderPlus(n int) []*raftNode {
	r := make([]*raftNode, 0, n+1)
	ldr := c.Leader(time.Second)
	if ldr != nil {
		r = append(r, ldr)
	}
	if len(r) >= n {
		return r
	}
	for _, node := range c.nodes {
		if !containsNode(r, node) {
			r = append(r, node)
			if len(r) >= n {
				return r
			}
		}
	}
	return r
}
// LeaderPlus returns the leader + n additional nodes from the cluster
// the leader is always the first node in the returned slice.