message: [swarm]: wait for node to exit on drop
  So that code afterwards can safely assume the db is no longer being written.
diff: @@ -43,6 +43,7 @@ impl Drop for LibraNode {
  if let Err(e) = self.node.kill() {
  panic!("LibraNode process could not be killed: '{}'", e);
  }
  + self.node.wait().unwrap();
  }
  }
  }
  