image-oci: add multi-layer OCI support and CMD default

Add support for multi-layer OCI images, enabling base + app layer builds:

Multi-layer support:
- Add OCI_BASE_IMAGE variable to specify base layer (recipe name or path)
- Add OCI_BASE_IMAGE_TAG for selecting base image tag (default: latest)
- Resolve base image type (recipe/path/remote) at parse time
- Copy base OCI layout before adding new layer via umoci repack
- Fix merged-usr whiteout ordering issue for non-merged-usr base images
  (replaces problematic whiteouts with filtered entries to avoid Docker
  pull failures when layering merged-usr on traditional layout)

CMD/ENTRYPOINT behavior change:
- Add OCI_IMAGE_CMD variable (default: "/bin/sh")
- Change OCI_IMAGE_ENTRYPOINT default to empty string
- This makes `docker run image /bin/sh` work as expected (like Docker Hub images)
- OCI_IMAGE_ENTRYPOINT_ARGS still works for legacy compatibility
- Fix shlex.split() for proper shell quoting in CMD/ENTRYPOINT values

The multi-layer feature requires umoci backend (default). The sloci backend
only supports single-layer images and will error if OCI_BASE_IMAGE is set.

Example usage:
  OCI_BASE_IMAGE = "container-base"
  IMAGE_INSTALL = "myapp"
  OCI_IMAGE_CMD = "/usr/bin/myapp"

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

0 files changed, 0 insertions, 0 deletions