Back-port for flatcar-3066 branch.
This change introduces a containerised SDK as a replacement for cork SDK
operations. It also simplifies versioning by removing the need for
manifest repos as well as usage of the "repo" tool by use of git
submodules for coreos-overlay and portage-stable.
The following feature scripts are added:
- run_sdk_container: Run a command in an SDK container, using the
current scripts repo + ebuild submodules.
current scripts repo + ebuild submodules.
- bootstrap_sdk_container / build_sdk_container_image: Bootstrap a new
SDK and create an SDK container from the resulting SDK tarball.
The following additions have been made to SDK scripts:
- setup_board: add --pkgdir parameter to use a custom binary packge
directory.
