At this moment ( 8.0.0-beta16 ) to switch to file configuration before install Drupal:
Into settings.php
Uncomment
$settings['bootstrap_config_storage'] = array('Drupal\Core\Config\BootstrapConfigStorageFactory', 'getFileStorage');
then add:
$config_directories = array(
CONFIG_ACTIVE_DIRECTORY => 'PATH_OUTSIDE_WEB_ROOT/config/active/',
CONFIG_STAGING_DIRECTORY => 'PATH_OUTSIDE_WEB_ROOT/config/staging/',
);
In sites/default/services.yml
add:
services:
config.storage:
class: Drupal\Core\Config\CachedStorage
arguments: ['@config.storage.active', '@cache.config']
config.storage.active:
class: Drupal\Core\Config\FileStorage
factory: Drupal\Core\Config\FileStorageFactory::getActive