CiviCRM 5.9.1 Cannot Read Database Information
Your DB connection specifies mysql://, and you are using PHP7.2. The MySQL extension was deprecated in PHP 5.5 and removed in PHP 7.0.

Try switching the two DB connect strings in civicrm.settings.php to use mysqli:// instead of mysql:// and see if that resolves the issue.

I would also remove any other changes (eg the addition of port :3306), to eliminate issues caused by other attempts to fix things.

If this resolves it, the cause was the migration from a PHP5 server to a PHP7 server, not an upgrade to CiviCRM 5.9.1.