message: remove Drop impl for LibraHandle, created shutdown method instead, and call shutdown from test code
diff: @@ -9,10 +9,16 @@ use libra_genesis_tool::config_builder::ValidatorBuilder;
  pub struct Node {
  pub config: NodeConfig,
  pub root_key: libra_crypto::ed25519::Ed25519PrivateKey,
  - _node: libra_node::main_node::LibraHandle,
  + node: libra_node::main_node::LibraHandle,
  _temp_dir: libra_temppath::TempPath,
  }
  +impl Drop for Node {
  + fn drop(&mut self) {
  + self.node.shutdown();
  + }
  +}
  +
  impl Node {
  pub fn start() -> Result<Self> {
  let temp_dir = libra_temppath::TempPath::new();
  @@ -34,7 +40,7 @@ impl Node {
  Ok(Self {
  root_key,
  config,
  - _node: node,
  + node,
  _temp_dir: temp_dir,
  })
  }
  