Timeout when max-childrens reached.

Description

Referring to:
https://bz.apache.org/bugzilla/show_bug.cgi?id=66603

It will be nice to set a timeout limit when connection will be terminated after trying to get free childrens of php-fpm. These limit should be smaller then max_execution_time or apache's timeouts because it will help with durability durring ddos attacks or with bugged apps. It specially important for shared servers, while one of app will reached max-childrens and there will be still incomming connections, so with waiting for childrens in infinity time or 300 seconds like apaches do it's to long and another limit's of server can be reached. These connections must be terminated alot faster, and timeout of http server cannot be smaller because of max_execution_time.

まず、max_children に到達した後に PHP-FPM が待機する問題についてのリンク先の Bugzilla レポートを読み、次に PHP-FPM の接続と子プロセス管理のエントリポイントを特定します。関連するテストを特定する前に、設定可能なタイムアウトの動作とその失敗ケースを定義します。既存の実行タイムアウトや HTTP タイムアウトの動作を変更せずに、過負荷状態の接続がその制限時間内に終了すれば完了です。