We were using Debian but Alpine more consistent. Use nested build.
Currently extract the hash in a nasty way but this can be fixed later
when we switch over hashing method.
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>
