[wip] oem: provide akamai (linode) images

[tormath1]

In this PR we add support for Akamai images:

• Build oem-scaleway with nothing inside
• Provide raw Akamai images
• https://github.com/flatcar/init/pull/117

:warning: This is currently experimental and only for testing purposes. :warning: (currently testing the Ignition PR: https://github.com/coreos/ignition/pull/1841 and https://github.com/coreos/afterburn/pull/1062)

How to use

Images should be available under: https://bincache.flatcar-linux.net/images/amd64/9999.0.6+tormath1-linode/

Testing done

• [ ] Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• [ ] Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.
• [ ] CI: http://jenkins.infra.kinvolk.io:8080/job/container/job/packages_all_arches/3907/cldsv/