graceid is not in alert when type is event_added

A keyerror was generated when processing an event_added alert type. The code is orchestrator.py, line 60. See https://emfollow.ligo.caltech.edu/sentry/gwcelery/issues/178/?query=is:unresolved

It looks like this alert type does not have a graceid key. It seems to only be needed if the DQV label has already be added to the superevent. I'm not sure what these lines are supposed to be doing, so it's a bit tricky to know the solution.