Add testing for OCI hooks

[sondavidb]

What is the problem you're trying to solve

Looking in pkg/ocihook, we don't seem to have to have any tests to ensure these OCI hooks are working as intended. We have one test in container_run_test.go, but nothing more extensive than that.

Describe the solution you'd like

Add more extensive testing to ensure OCI hooks are working properly.

Additional context

No response

[apostasie]

Yes, we need this one way or the other (@AkihiroSuda can we tag this "CI area" or "testing" or something in the line?).

I have been doing work recently inside oci-hooks, and debugging anything in there, at the intersection of containerd/runc/cni-plugins/oci-hooks is a major brainf.