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.

Start by reading the linked Bugzilla report about PHP-FPM waiting after max_children is reached, then locate the PHP-FPM connection and child-management entry points. Define the configurable timeout behavior and its failure cases before identifying the relevant tests; done means overloaded connections terminate within that limit without changing the existing execution or HTTP timeout behavior.