Fixes ServiceRestarter to not block event-listener thread

- Previously RestarterPolicy called entity.restart inside the
  event-listener thread. That caused all other events for that entity's
  subscriptions to be queued until that entity's single event handler
  thread was free again.
- Particularly bad if service-up is triggered by an event-subscription,
  so that never happens causing entity.restart to fail!
Fixes ServiceReplacer to not block event-listener thread