提供一个接口，在服务发现准备好之前，等待准备好

[gaohuag]

What would you like to be added:
提供一个接口，在服务发现准备好之前，等待准备好
Why is this needed:
目前的策略是sleep 3s,见代码：
"""
func init() {
config.Load()
referenceConfig.GenericLoad(appName) //appName is the unique identification of RPCService
time.Sleep(3 * time.Second)
}
"""

[LaurenceLiZhixin]

I updated the default reference config's check field to true, and consumerConfig would wait for invoker ready until timeout.
Refer to #1531