fix(rocklet): skip kata dind setup when docker data-root cannot be created

[hzy123662]

Summary

• check permissions before creating the Docker data-root for Kata DinD;
• log a clear warning and skip unavailable Kata DinD steps without returning early from setup_kata_dind;
• preserve writable multi-level custom Docker data-root paths.

Problem

When a sandbox image uses a non-root default user, docker_run.sh cannot create /var/lib/docker.

Because the script enables set -o errexit, the permission error terminates the startup script before Rocklet starts.

Implementation

When the Docker data-root does not exist, walk upward to find the nearest existing path and verify that it is:

• a directory;
• writable;
• executable/traversable.

If the directory cannot be created, the script only prints a warning. The DinD mkdir, mknod, and mount steps run only when the Docker data-root exists, so setup_kata_dind reaches its normal end and the subsequent Rocklet startup continues.

Test Plan

• bash -n rock/rocklet/local_files/docker_run.sh
• git diff --check
• tests/unit/deployments/test_docker_env_injection.py: 8 passed
• non-root + Kata + non-writable /var/lib/docker: warning emitted, directory not created, Rocklet startup marker observed, exit code 0
• non-root + Kata + writable multi-level custom data-root: directory created and exit code 0
• non-root + non-Kata: existing behavior unchanged
• mount and mknod mocked during local permission tests

No automated Shell test file was added because existing changes to setup_kata_dind and docker_run.sh use script-level and integration validation rather than a dedicated Shell unit-test framework. The existing Docker environment-injection unit suite was run as regression coverage.

Real Kata runtime validation still needs to be performed on a Kata-enabled Linux worker.

refs #1308

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