Fix Bug #67530 	error_log=syslog ignored

As for Bug #64915
Systemd use --nodaemonize but need to error_log to file or syslog to be honoured
Fix Bug #67531 	syslog cannot be set in pool configuration

error_log is listed in FPM_PHP_INI_TO_EXPAND,
but should not be expand when value = syslog
NEWS