func (m *Member) PickPeerURL() string {
	if len(m.PeerURLs) == 0 {
		panic("member should always have some peer url")
	}
	return m.PeerURLs[rand.Intn(len(m.PeerURLs))]
}
func (m *Member) PickPeerURL() string {
	if len(m.PeerURLs) == 0 {
		panic("member should always have some peer url")
	}
	return m.PeerURLs[rand.Intn(len(m.PeerURLs))]
}
// PickPeerURL chooses a random address from a given Member's PeerURLs.
// It will panic if there is no PeerURLs available in Member.