Because we are not yet using the image store, this requires a
patched `ctr` that can run a specified rootfs rather than an
image.
We will switch to the image store later, but this requires
extensive build changes.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
Also add ca-certificates to base, needed to use `dist` to pull.
Make two stage builds for `containerd` and `runc` so they have a
from `scratch` second stage.
Signed-off-by: Justin Cormack <justin.cormack@docker.com>
