package_to_container: Bundle container config files into squashfs

This puts the config.json and runtime.json files directly
into the container squashfs.

BUG=none
TEST=Run package_to_container, mount the resulting squashfs, and
verify that /config/config.json and /config/runtime.json are
there.

Change-Id: I0f47305befc26e064746a8b21180b09a37c0ba50
Reviewed-on: https://chromium-review.googlesource.com/368458
Commit-Ready: Keshav Santhanam <ksanthanam@google.com>
Tested-by: Keshav Santhanam <ksanthanam@google.com>
Reviewed-by: Dylan Reid <dgreid@chromium.org>
3 files changed