message: docker: don't try to add yet another use
  Instead just switch to it.
diff: if [ -n "${LOCAL_USER_ID}" ]; then
  echo "Starting with UID: $LOCAL_USER_ID"
  - useradd --shell /bin/bash -u $LOCAL_USER_ID -o -c "" -M user
  + usermod -u $LOCAL_USER_ID user
  export HOME=/home/user
  chown -R user:user $HOME
  