fix custom log writer returned bytes written count

It was including the prefixed datetime string in the byte count which
made it longer than the passed in byte slice and the io.Multiwriter
considers that an error and stops processing the writers at that point
(skipping the syslog writer).

logging/logging.go

@@ -32,7 +32,10 @@ func (writer logWriter) Write(bytes []byte) (int, error) {
 	if len(bytes) == 0 {
 		return 0, nil
 	}
-	return fmt.Fprintf(writer.out, "%s %s", now(), bytes)
+	if _, err := fmt.Fprintf(writer.out, "%s %s", now(), bytes); err != nil {
+		return 0, err
+	}
+	return len(bytes), nil
 }
 
 // Config is the configuration for this log setup.