When an image did not provide a build script, due to a broken link for
instance, the build-all-docker-images script was wrongly marking the
image as "up-to-date", and the functional gate was reporting success.
This commit restores the expected behavior, and mark the images with
non-existent build scripts as failures.
Change-Id: Ifedc8d9c312925fe5aa953ed8f8fdae02b756906
Closes-Bug: #1460959
9a5fed6608