WasmEdge plugins are loaded from the container's rootfs and not from the host

> Just bear in mind that the env-vars you are parsing are those in the container spec, and not those of the shim.
> Also the plugin is loaded from the container's rootfs, and not from the host.
> I'm happy to merge as is, and discuss if we want to switch to loading from the host in a different issue / PR.

_Originally posted by @jprendes in https://github.com/containerd/runwasi/pull/877#pullrequestreview-2680072411_