Use consistent naming in release artifacts

[texasmichelle]

Consistently name release artifacts.

• Add kubeflow- to archive name. This makes it easier to identify the source of the downloaded file.
• Do not strip v from version in unpacked artifact. This is consistent with version tags in the repo.

Example:
Latest release asset is named v0.3.5, but unpacked folder is named kubeflow-0.3.5:

$ wget https://github.com/kubeflow/kubeflow/archive/v0.3.5.tar.gz
$ tar -xvf v0.3.5.tar.gz
$ ls
kubeflow-0.3.5

[jlewi]

I'm not sure how much control we have here.

I think the name "v0.3.5" is based on the release tag.

The tarball is autogenerated from the source tree as well by GitHub.

[texasmichelle]

Oh right - because we're not generating binaries, this is an automated GH thing. Consistency across all of GH makes it less of an issue.