ISLE docker-compose.yml - 1.2.7.1 - Import existing Drupal database

Description:
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This line defines a Docker 'volume' that can be used to import an existing Islandora's Drupal database.  Once a database has been imported the volume will persist and need not be imported again. Once your data is imported it is placed into the 'db_data' volume.  See 1.2.7.2, https://gist.github.com/McFateM/089b18a1b2e5c1432751d481fd1b6112, for 'db_data' details.

Instructions:
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Make sure the line in docker-compose.yml is initially NOT a comment. 
Export your existing Islandora Drupal database.  I did this using Drush from a terminal opened on my production Islandora server, like so:
      cd /var/www/drupal7/sites/default
      drush sql-dump > drupal.sql
      
Now, copy (or move) your dumped Drupal database to the ../mysql/data folder in your ISLE project on your host.  My command was:      
      rsync -aurvi drupal.sql user@host:/home/user/Projects/Docker/dg_isle_docker/dg/mysql/data/

Use:
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After you have successfully done a 'docker-compose up' command you may edit this line in your docker-compose.yml and comment it out by adding a hashtag at the start of the line like so:
      # - ./dg/mysql/data:/sql_databases_for_import    

Notes:
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Ben's original comment... "I placed my sql.gz files in here and used phpmyadmin or mysql -uroot -p<MYSQL_ROOT_PASSWORD> <database> < drupal.sql"