Don't compress the archive made from git's output.

Commit 894d4a23fba made BuildFile use TarSum, which doesn't support
compressed tar archives.
This breaks builds from git url, which compressed it with bzip2.
Instead, just pass it uncompressed.

Docker-DCO-1.0-Signed-off-by: Paul Lietar <paul@lietar.net> (github: plietar)
Merge pull request #3535 from plietar/3457-git-build

Don't compress the archive made from git's output.