Comment 3 for bug 1821344

Reviewed: https://review.openstack.org/649643
Committed: https://git.openstack.org/cgit/openstack/stx-config/commit/?id=d1536ac9dfbb0d17a6fd30d61f76deb0dee57594
Submitter: Zuul
Branch: master

commit d1536ac9dfbb0d17a6fd30d61f76deb0dee57594
Author: Angie Wang <email address hidden>
Date: Wed Mar 27 10:10:32 2019 -0400

    Fix the image download issue if unknown image ever specified

    We have a yaml file which has a section "download_images" stores
    the required images. The required images list will be regenerated
    when applying application. The current logic is to extend the stored
    image list with the newly generated image list which causes the
    application apply to always fail if the user ever specifies an
    unknown image. The extend should be removed.

    Change-Id: I6ee031c7f866ab213e2ef8204c1f829567dcb376
    Closes-Bug: 1821344
    Signed-off-by: Angie Wang <email address hidden>