ostree-fetcher-curl: retry requests that fail except 404s.

This will return G_IO_ERROR_TIMED_OUT with any http call
that fails except on cases were a response is received
with a 404 status code. This will trigger a retry.

src/libostree/ostree-fetcher-curl.c

@@ -329,7 +329,7 @@ check_multi_info (OstreeFetcher *fetcher)
             }
           else
             {
-              g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_FAILED,
+              g_task_return_new_error (task, G_IO_ERROR, G_IO_ERROR_TIMED_OUT,
                                        "While fetching %s: [%u] %s", eff_url, curlres,
                                        curl_easy_strerror (curlres));
               _ostree_fetcher_journal_failure (req->fetcher->remote_name,