message: update_agent: log finalization success
  This logs an info message when a finalization attempt completes
  successfully. Previously we were only updating the live service
  status, but this makes it easier to gather the actual timestamp
  for such event (from journal).
diff: @@ -392,8 +392,10 @@ impl UpdateAgentInfo {
  match self.finalize_deployment(release).await {
  Ok(release) => {
  FINALIZATION_SUCCESS.inc();
  - utils::update_unit_status(&format!("update finalized: {}", release.version));
  + let status_msg = format!("update finalized: {}", release.version);
  + log::info!("{}", &status_msg);
  state.update_finalized(release);
  + utils::update_unit_status(&status_msg);
  }
  Err(e) => log::error!("failed to finalize deployment: {}", e),
  }
  @@ -401,10 +403,10 @@ impl UpdateAgentInfo {
  /// Actor job is done.
  async fn tick_end(&self, state: &mut UpdateAgentMachineState, release: Release) {
  - let status = format!("update applied, waiting for reboot: {}", release.version);
  - log::info!("{}", status);
  + let status_msg = format!("update applied, waiting for reboot: {}", release.version);
  + log::info!("{}", &status_msg);
  state.end();
  - utils::update_unit_status(&status);
  + utils::update_unit_status(&status_msg);
  }
  /// Fetch and stage an update, in finalization-locked mode.
  