make taskworker console.* log to file and not stdout

this is similar to code in box.js

src/taskworker.js

@@ -43,15 +43,10 @@ const taskId = process.argv[2];
 const logFile = process.argv[3];
 
 function setupLogging(callback) {
-    fs.open(logFile, 'a', function (error, fd) {
-        if (error) return callback(error);
+    const logfileStream = fs.createWriteStream(logFile, { flags:'a' });
+    process.stdout.write = process.stderr.write = logfileStream.write.bind(logfileStream);
 
-        require('debug').log = function (...args) {
-            fs.appendFileSync(fd, util.format(...args) + '\n');
-        };
-
-        callback();
-    });
+    callback();
 }
 
 // Main process starts here