fix(node): validate OCI loader tools at boot

Hyper.Img.OciLoader.test_system/0 (checks skopeo/umoci/mke2fs) existed but was
never called from Hyper.Node.test_system, so a missing skopeo only surfaced at
image-load time. Wire it in after Umoci.ensure_installed so the node refuses to
boot when an OCI loader tool is absent, like every other host requirement.

Author: markovejnovic

lib/hyper/node.ex

@@ -151,6 +151,7 @@ defmodule Hyper.Node do
          :ok <- Hyper.Node.FireVMM.VmLinux.Provider.ensure_installed(),
          :ok <- Hyper.Node.Vmlinux.test_system(),
          :ok <- Hyper.Img.OciLoader.Umoci.ensure_installed(),
+         :ok <- Hyper.Img.OciLoader.test_system(),
          :ok <- Hyper.Node.Users.test_system(),
          :ok <- Hyper.Node.Layer.Repo.test_system(),
          :ok <- Hyper.SuidHelper.test_system(),