utils/tarsum* -> pkg/tarsum

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
move testdata to tarsum package.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
utils.Debugf -> fmt.Printf

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Merge pull request #7324 from erikh/move_tarsum

Move tarsum to pkg/