title: Host 'X' is not allowed to connect to this MySQL server
body: <p>I wanna deploy MySQL+PHPMyAdmin. My docker-compose.yml:</p>
  
  <pre><code>version: "3"
  services:
    db:
      image: mysql:5.7
      restart: always
      container_name: db
      volumes:
        - ./~mysql:/var/lib/mysql
        - ./mysql.cnf:/etc/mysql/conf.d/my.cnf
      environment:
        MYSQL_DATABASE: "dbtest"
        MYSQL_ROOT_PASSWORD: "123456"
        MYSQL_ROOT_HOST: "%"
      networks:
        - db
      command: --default-authentication-plugin=mysql_native_password
      healthcheck:
        test: "mysqladmin ping -h localhost"
        interval: 1s
        timeout: 1s
        retries: 60
  
    phpmyadmin:
      image: phpmyadmin/phpmyadmin:4.7
      restart: always
      container_name: phpmyadmin
      ports:
        - 8080:80
      networks:
        - external-net
        - db
      environment:
        PMA_HOST: db
      depends_on:
        - db
  
  networks:
    external-net:
      external:
        name: external-net
    db:
      driver: bridge
  </code></pre>
  
  <p>After some time later I getting subject error. MYSQL_ROOT_HOST don't helped. When I trying to connect to mysql from db-container:</p>
  
  <pre><code>ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
  </code></pre>
  
  <p>I really don't know what to do with this magic... Thx.</p>