Reinit grpc client when client not found

[yuwmao]

When a follower recovers from the network issue, it needs to fetch data from the leader, but it may encounter "Failed to find client" error and fail the request which makes PG laggy. To handle this, we have to restart the process as the workaround currently. Need to reinit grpc client when not found.

[xiaoxichen]

we also see similar issues if CM is down, will that be covered by this issue?

[yuwmao]

Yes, this was found in isofruit-cherry where cm had went down for some time and after cm recovered, the leader recovered and appended logs to follower, but follower can not fetch data.