Update `mysql` commands to use `mariadb`

```
drupal-1  | Validating Database credentials
drupal-1  | mysqladmin: Deprecated program name. It will be removed in a future release, use '/usr/bin/mariadb-admin' instead
drupal-1  | mysqld is alive
drupal-1  | Credentials are valid
drupal-1  | mysql: Deprecated program name. It will be removed in a future release, use '/usr/bin/mariadb' instead
```