Verbose mode

When for whatever reason an error keeps occurring and needs some back and forth, it's a bit inconvenient to run the curl command, copy the log location, and tail it repeatedly. It would be nice if we had an environment variable to make the script print everything it writes in logs, directly to stdout.

Also when it is retrying to fetch a url, it may take a few minutes until the process finishes and prints the location of the log file, while if it printed the errors in stdout simultaneously (when the environment variable is set) one could immediately see it is a network error and act, saving time.

この issue にはファイル、テスト、エントリーポイントが記載されていません。まず installer の logging と URL-retry のコードを見つけ、次にログ出力がどのようにファイルへ到達するか、またログの場所がいつ出力されるかを追跡します。環境変数で制御される verbose モードが、retry 中のログエラーを stdout にも出力し、通常の出力を変更しなければ完了です。