message: update_agent: fix timestamp in status updates
  This fixes status updating logic, in order to display the timestamp
  of the last check (instead of the last state change).
diff: @@ -222,6 +222,11 @@ impl UpdateAgent {
  let state_change = self
  .local_deployments()
  .then(|res, actor, _ctx| {
  + let timestamp_now = chrono::Utc::now();
  + update_unit_status(&format!(
  + "periodically polling for updates (last checked {})",
  + timestamp_now.format("%a %Y-%m-%d %H:%M:%S %Z")
  + ));
  let allow_downgrade = actor.allow_downgrade;
  let release = match res {
  Ok(depls) => {
  @@ -241,10 +246,6 @@ impl UpdateAgent {
  }
  None => {
  actor.state.no_new_update();
  - update_unit_status(&format!(
  - "periodically polling for updates (last checked {})",
  - &actor.state_changed.format("%a %Y-%m-%d %H:%M:%S %Z")
  - ));
  }
  };
  Ok(())
  