Ensures all known volumes (known b/c they are persisted to disk) have
their volume drivers refcounted properly.
In testing this, I found an issue with `--live-restore` (required since
currently the provided volume plugin doesn't keep state on restart)
where restorted plugins did not have a plugin client loaded causing a
panic when trying to use the plugin.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
