Description
When configuring DFS with DFS NFS path and not using another Database, generic.php file trying to use not existing parameters e.g. database_host, database_port, also if dfs_db_port is null (default) then generic.php file thinking dfs_db_port it's not defined

Steps to reproduce
1. Install clean eZ Platform v3

2. Configure only DFS_NFS_PATH

3. Try to enter the site

Actual
Show error message: 

You have requested a non-existent parameter "database_host". Did you mean this: "database_charset"? in /var/www/html/config/packages/overrides/generic.php (which is loaded in resource "/var/www/html/config/packages/overrides/generic.php").

Expected result
The site will load correctly without errors and DFS will use default DB