test: Fix fuser invocation in directory cleanup

stdout gets captured by Machine.execute(). Write the fuser output to
stderr so that we can actually see it.

Also cover the directory itself, not just its contents.

test/common/testlib.py

@@ -2049,7 +2049,7 @@ def restore_dir(self, path: str, post_restore_action: Optional[str] = None, rebo
             if path.startswith("/home"):
                 cmd = f"umount -lf {path}"
             else:
-                cmd = f"umount {path} || {{ fuser -uvk {path}/* || true; sleep 1; umount {path}; }}"
+                cmd = f"umount {path} || {{ fuser -uvk {path} {path}/* >&2 || true; sleep 1; umount {path}; }}"
             self.addCleanup(self.machine.execute, cmd)
 
     def restore_file(self, path: str, post_restore_action: Optional[str] = None):