Build kernel release archives for use in building RancherOS

To build the tgz's and the kernel header & extras images, run:

KERNEL_TAG=4.9.10 make release

and if you're uploading them, set your GITHUB_TOKEN and login to docker hub, then run

(this requires https://github.com/aktau/github-release to be installed in your path)

dist/publish.sh

packaging your own kernel builds

Assuming you have some kernel source you have built in /usr/src/linux-4.8, you can package up the result by running

./scripts/package-kernel --srcdir /usr/src/linux-4.8

You may need to adjust the expected module list files.