Ingest spawn output in realtime, processing stdout/stderr as the spawned command emits output.

exec_realtime_io.js

 exec_realtime_io(cmd,log_cb,param_array,process_stdout_cb,process_stderr_cb,close_cb) {
        var stdout='';
        var stderr='';
        log_cb(`running ${cmd} ${param_array}`);
        var c = spawn(cmd,param_array);
        c.stdout.on('data',(data)=> { stdout+=data; process_stdout_cb(data); });
        c.stderr.on('data',(data)=> { stderr+=data; process_stderr_cb(data); });
        c.on('close',(code)=>{ close_cb(code, stdout, stderr);});
    }