spoa server fails to build when python3.8 is not available. If
python3-config --embed fails, the output of the command is registered in
check_python_config. However when it's later used to define
PYTHON_DEFAULT_INC and PYTHON_DEFAULT_LIB it's content does not match
and fallback to python2.7
Content of check_python_config when building with python3.6:
Usage: bin/python3-config --prefix|--exec-prefix|--includes|--libs|--cflags|--ldflags|--extension-suffix|--help|--abiflags|--configdir python3
As we are only looking for return code, this commit ensure we always
ignore the output of python3-config or hash commands.
54f7823ed5