Do not retry refreshSources when region server is already stopping

Found this when debugging HBASE-28114, it is designed to retry forever but when aborting a region server, we will stop the rpc client, and it will retry a lot of times and output a lot of logs, which even cause the Jenkins job OOM…

I think we should throw the exception out directly and give up retry when aborting the region server.

==== Updated ====

It turns out that the problem is the retry when initialize new shipper failed. We should stop retrying when region server is already stopped.