Fix invalid argument error on push

With 32ba6ab from #9261, TempArchive now closes the underlying file and
cleans it up as soon as the file's contents have been read. When pushing
an image, PushImageLayerRegistry attempts to call Close() on the layer,
which is a TempArchive that has already been closed. In this situation,
Close() returns an "invalid argument" error.

Add a Close method to TempArchive that does a no-op if the underlying
file has already been closed.

Signed-off-by: Andy Goldstein <agoldste@redhat.com>
There is `ioutil.NopCloser` exactly for this.