Fix to close pipe when ping command exits with failure
Fix to close pipe when ping command exits with failure

This bug causes pipe open error: Too many open files, which
leads to failure of connecting to trusted servers, and then
pgpool goes to down status.

treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres,treasure-data/prestogres