list:map[int32][]func(string,string)
          回调map

     watchEventMutex sync.RWMutex
          map锁

     addWatchCallbacks(eventType:int32,callback:func(etcdPath:string,addr:string))
          添加回调，eventType是类型，比如：clientv3.EventTypePut或者clientv3.EventTypeDelete。callback就是具体的方法咯

     invokeWatchCallBacks(eventType int32,etcdPath:string,addr:string)
          执行回调

单例
     watchCallbackMgr:WatchCallbackMgr