@Override
    public void onClusterNodesChanged(List<RemoteInstance> remoteInstances) {
        refresh(remoteInstances);
    }
Compare clients between exist clients and remote instance collection. Move the clients into new client collection
which are alive to avoid create a new channel. Shutdown the clients which could not find in cluster config.
<p>
Create a gRPC client for remote instance except for self-instance.

@param remoteInstances Remote instance collection by query cluster config.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/remote/client/RemoteClientManager.java