超时实现 select 计时器
github.com\eclipse\paho.mqtt.golang@v1.4.3\token.go
// WaitTimeout implements the Token WaitTimeout method.
func (b *baseToken) WaitTimeout(d time.Duration) bool {
timer := time.NewTimer(d)
select {
case <-b.complete:
if !timer.Stop() {
<-timer.C
}
return true
case <-timer.C:
}
return false
}
