Include small MIT FastCGI client library from
https://github.com/adoy/PHP-FastCGI-Client

Add run_request function to easily run a FastCGI call,
which is needed for new tests.
Add various tests for FPM
- covering recent bugs (68420, 68421, 68423, 68428)
- for UDS
- for ping and status URI
- for multi pool and multi mode