title: Docker doesn't set MariaDB password
body: <p>In my docker-compose.yml </p>
  
  <pre><code>version: '3'
  services:
    db:
      image: mariadb:latest
      volumes:
        - ./dc_test_db:/var/lib/mysql
      restart: always
      environment:
        MYSQL_ROOT_PASSWORD: secret
  </code></pre>
  
  <p>When I connect via:</p>
  
  <pre><code>sudo docker exec -it docker_db_1 mysql -u root -p 
  </code></pre>
  
  <p>I have to let the password empty to login. What is wrong?</p>