Just a minor cleanup; use archive.Tar as we're not using other
options here.

Signed-off-by: Sebastiaan van Stijn <[email protected]>
(cherry picked from commit a8f83d5)
Signed-off-by: Sebastiaan van Stijn <[email protected]>

Currently the cp will tar from the same directory it will untar into
simultaneously. There is a race between reading the file and truncating
the file for write, however, the race will not show up with a large
enough buffer on the tar side if buffered before the copy begins.

Also removes the unnecessary deferred removal, the removal is handled by
cleanup and respects the no cleanup env.

Signed-off-by: Derek McGowan <[email protected]>
(cherry picked from commit 8c0cb30)
Signed-off-by: Sebastiaan van Stijn <[email protected]>