message: only allow one riot server instance simultaneously
diff: #!/bin/bash
  PORT=5000
  -echo "running riot on http://localhost:$PORT ..."
  BASE_DIR=$(readlink -f $(dirname $0))
  +PIDFILE=riot.pid
  +CONFIG_BACKUP=config.e2etests_backup.json
  +
  cd $BASE_DIR/
  +
  +if [ -f $PIDFILE ]; then
  + exit
  +fi
  +
  +echo "running riot on http://localhost:$PORT ..."
  pushd riot-web/webapp/ > /dev/null
  python -m SimpleHTTPServer $PORT > /dev/null 2>&1 &
  PID=$!
  popd > /dev/null
  -echo $PID > riot.pid
  +echo $PID > $PIDFILE
  