Add more unit test case for create_runtime_config()

[jiangliu]

The OCI image spec has defined the way to generate runtime configuration from images at https://github.com/opencontainers/image-spec/blob/main/conversion.md

So much more unit test cases are needed to ensure that we have strictly followed the spec.

[ariel-adam]

@jiangliu is this issue still relevant or can be closed?
If it's still relevant to what release do you think we should map it to (mid-November, end-December, mid-February etc...)?