Always include a file list for the image (ci-build script)

(Documenting after the fact)

For some situations it's useful to just quickly confirm if a file exists in the system. If publishing a small text file containing a file manifest then there's no need to download a large image or tarball to do such checks.

This was already provided by default in the buildhistory directory named files-in-image.txt so we just needed to stage that file.

In addition, the whole buildhistory directory is included among the published artifacts.

PR #109