title: RUN echo in Dockerfile with docker-compose fails
body: <p>So, I have the following docker-compose file:</p>
  
  <pre><code>version: "3"
  
  services:
    webserver:
      build: 
        context: ./bin/webserver
      container_name: 'png-webserver'
      restart: 'always'
      ports:
        - "18011:80"
        - "14431:443"
      links: 
        - mysql
      volumes: 
        - ${DOCUMENT_ROOT-./www}:/var/www/html
        - ${PHP_INI-./config/php/php.ini}:/usr/local/etc/php/php.ini
        - ${VHOSTS_DIR-./config/vhosts}:/etc/apache2/sites-enabled
        - ${LOG_DIR-./logs/apache2}:/var/log/apache2
    mysql:
      build: ./bin/mysql
      container_name: 'png-mysql'
      restart: 'always'
      ports:
        - "13306:3306"
      volumes: 
        - ${MYSQL_DATA_DIR-./data/mysql}:/var/lib/mysql
        - ${MYSQL_LOG_DIR-./logs/mysql}:/var/log/mysql
        - ./mysqlhome:/home
      environment:
        MYSQL_ROOT_PASSWORD: tiger
        MYSQL_DATABASE: nubuilder
        MYSQL_USER: deckoff
        MYSQL_PASSWORD: deeppurple
    phpmyadmin:
      image: phpmyadmin/phpmyadmin
      container_name: 'png-phpmyadmin'
      links:
        - mysql
      environment:
        PMA_HOST: mysql
        PMA_PORT: 3306
      ports:
        - '18080:80'
      volumes: 
        - /sessions
  </code></pre>
  
  <p>And the following Dockerfile ( for the mariadb container):</p>
  
  <pre><code>FROM mariadb:10.1
  
  RUN mysql --defaults-extra-file='/home/secret' nubuilder4 &lt; /home/nubuilder4.sql
  
  RUN apt-get update &amp;&amp; apt-get install -y nano 
  
  RUN bash -c 'echo [mysqld] &gt;&gt; /etc/mysql/my.cnf'
  RUN bash -c 'echo sql-mode=NO_ENGINE_SUBSTITUTION &gt;&gt; /etc/mysql/my.cnf'
  </code></pre>
  
  <p>In a nutshell - seems like RUN commands in the Dockerfile never run. I would expected the 2 lined appended to the file, and nano installed, but none of this happens. I have tried running them after starting the containers, and they work fine. Seems like I am doing something wrong.</p>
  
  <p>Also, I have no idea how to debug that.</p>