nodepath: move the node state root to /var/lib/ate (#1926)

Fixes #1911

`/var/lib/ateom-gvisor` was named when gVisor was the only sandbox
class; worker pods of both classes mount it. This renames
`nodepath.BasePath` to `/var/lib/ate` everywhere it is spelled out:
atelet's manifest, the kind CSI scripts, `ate-setup`'s CSI step, and the
docs. The controller's worker pod mounts follow the constant.

No compatibility path, per the comment above. A rolling upgrade rolls
the pools once at the controller step, and a worker that lands on a node
whose atelet still uses the old path reaches it only once that node
moves; `docs/upgrade.md` says so. The old directory can be deleted
afterwards.

- [x] Tests pass
- [x] Appropriate changes to documentation are included in the PR

hack/setup-csi-hostpath-kind.sh

@@ -43,13 +43,13 @@ echo "Using Kind node: ${KIND_NODE}"
 if docker ps | grep -q "${KIND_NODE}"; then
   # Unmount any stale mounts to prevent "device or resource busy"
   docker exec "${KIND_NODE}" sh -c '
-    for mnt in $(mount | grep /var/lib/ateom-gvisor | awk "{print \$3}"); do
+    for mnt in $(mount | grep /var/lib/ate | awk "{print \$3}"); do
       echo "Unmounting stale mount: ${mnt}"
       umount -f "${mnt}" || true
     done
   ' || true
   # Only delete contents, keep the directory itself to preserve mounts of running pods (like atelet)
-  docker exec "${KIND_NODE}" sh -c 'rm -rf /var/lib/ateom-gvisor/*' || true
+  docker exec "${KIND_NODE}" sh -c 'rm -rf /var/lib/ate/*' || true
 else
   echo "Warning: Kind node ${KIND_NODE} not running. Skipping directory cleanup."
 fi
@@ -98,12 +98,12 @@ spec:
       - name: hostpath
         volumeMounts:
         - name: ateom-dir
-          mountPath: /var/lib/ateom-gvisor
+          mountPath: /var/lib/ate
           mountPropagation: Bidirectional
       volumes:
       - name: ateom-dir
         hostPath:
-          path: /var/lib/ateom-gvisor
+          path: /var/lib/ate
           type: DirectoryOrCreate
 "
 

hack/setup-csi-nfs-kind.sh

@@ -48,12 +48,12 @@ spec:
       - name: nfs
         volumeMounts:
         - name: ateom-dir
-          mountPath: /var/lib/ateom-gvisor
+          mountPath: /var/lib/ate
           mountPropagation: Bidirectional
       volumes:
       - name: ateom-dir
         hostPath:
-          path: /var/lib/ateom-gvisor
+          path: /var/lib/ate
           type: DirectoryOrCreate
 '