message: update_agent: Delay if transitioning btwn Steady & NoNewUpdates
  Generally, state changes trigger immediate ticks; make an exception
  for the case where we're transitioning from ReportedSteady to
  NoNewUpdates. This will prevent Zincati from performing the first
  two polls for updates consecutively with no delay in between.
diff: @@ -113,8 +113,13 @@ impl UpdateAgent {
  // State changes trigger immediate tick/action.
  if discriminant(&prev_state) != discriminant(&self.state) {
  + // Unless we're transitioning from ReportedSteady to NoNewUpdate.
  + if !(prev_state == UpdateAgentState::ReportedSteady
  + && self.state == UpdateAgentState::NoNewUpdate)
  + {
  return None;
  }
  + }
  let delay = match self.state {
  UpdateAgentState::ReportedSteady | UpdateAgentState::NoNewUpdate => {
  