tar packer

I need an implementation (and interface) that constructs a tar.gz from:

• the contents of working-dir (excluding existing tars)
• the repositories folder from the cache's localstorage
• all blobs listed in the list that the function gets from the input
• the imagesetconfig

Tar contents:

• docker/v2/repositories : manifests for all mirrored images
• docker/v2/blobs/sha256 : blobs that haven't been mirrored (diff)
• working-dir
• image set config

Diff logic: