Makes config download write directly to the directory specified by
--config-dir, instead of a tmpdir underneath that location.
This change also breaks Config.download_config tasks into unique
funtions to support accessing directory creation functionality
independently from config retrieval and playbook creation.
Change-Id: Ie00f71b12f56262985c47810be0e80402e9e558e
Depends-On: Ibb59b044dc0c14bf48dc3d500536195230414c81
Depends-On: Icbd6dd65893f785b7ca8edf2eab46dbc7492e050
Closes-Bug: 1752118
f8aa548ca6