[cdc_stream] Append errors from netstart to status (#9)

So far, errors from the remote netstat process would only be logged in
the asset stream service, for instance when SSH auth failed. However,
the errors were not shown to the client, and that's the most important
thing.

Also adds some feedback to cdc_stream in case of success.

asset_stream_manager/session.cc

@@ -76,7 +76,7 @@ absl::Status Session::Start(int local_port, int first_remote_port,
       ports,
       PortManager::FindAvailableRemotePorts(
           first_remote_port, last_remote_port, "127.0.0.1", process_factory_,
-          &remote_util_, kInstanceConnectionTimeoutSec, true),
+          &remote_util_, kInstanceConnectionTimeoutSec),
       "Failed to find an available remote port in the range [%d, %d]",
       first_remote_port, last_remote_port);
   assert(!ports.empty());