Store kernel build logs

[emkll]

We should redirect/tee the output of the Makefile command that builds the kernel to a file, and persist that file on disk/outside of the build container to ensure we can archive the kernel build logs.

[conorsch]

Until we've got a solution for this problem, let's just document the terminal output we do have, plus the checksums of the created artifacts, and store that in the build-logs repo.

In terms of addressing the problem... do we really need Ansible here anymore? We're already building in a docker container, so falling back to that strategy would make it simple to capture the verbose output of the full kernel build. Most of the value we get out of Ansible is the grsec URL munging in https://github.com/freedomofpress/ansible-role-grsecurity-build/blob/522a0c525a68f34fef239269ef73d13c1b25caec/library/grsecurity_urls.py, but that's Python already, and shouldn't be a big deal to port into a dockerfile.