This commit does a few things to decouple the artifacts from mongodb. - Creates an ArtifactFileDB which stores artifacts in a json file on the local machine - Adds tests fro the artifact file DB - Sets the file database to be default if pymongo isn't installed - Extends the Artifact class to prepare for downloading artifacts from gem5-resources Change-Id: I1bceef94dc53c066d1c0475e79c9a1ad1f1a6202 Signed-off-by: Jason Lowe-Power <jason@lowepower.com> Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/47463 Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu> Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu> Tested-by: kokoro <noreply+kokoro@google.com>