Unexpected EOF when retry to download

[JulienBalestra]

Describe what happened:

I canceled a download because of a poor bandwidth.

I restarted it.

I got this issue:

I0620 15:33:07.825652    4272 binary.go:87] Archive already here: /home/jb/go/src/github.com/DataDog/pupernetes/sandbox/bin/hyperkube-v1.10.3.tar.gz
I0620 15:33:07.825703    4272 binary_hyperkube.go:17] Extracting /home/jb/go/src/github.com/DataDog/pupernetes/sandbox/bin/hyperkube-v1.10.3.tar.gz
E0620 15:33:15.398543    4272 binary_hyperkube.go:21] Cannot untar /home/jb/go/src/github.com/DataDog/pupernetes/sandbox/bin/hyperkube-v1.10.3.tar.gz, 
gzip: stdin: unexpected end of file
tar: Unexpected EOF in archive
tar: Error is not recoverable: exiting now
: exit status 2
E0620 15:33:15.398614    4272 main.go:27] Exiting on error: 1

To bypass it, I needed to remove manually the incomplete archive.
We could remove the archive anyway and re-download it again.

[JulienBalestra]

This is addressed by #74