Fix tests for events

[philrz]

After merging an unrelated enhancement, the Travis run showed the delete_event example failed. I traced it down to an event in the backend that's failing delete reasons yet to be explained (event ID=413658984227033090). However, it was an event that shouldn't have been flagged by delete_event in the first place. That is, the post_event examples were creating events with names "test event name" and delete_event was targeting all events with name "test event". However, I think due to the way ES search works, this was actually matching all items with names matching test OR event, which is why it was finding this rogue/unrelated event that wouldn't delete. I've now tightened all of this up by using underscores to make single-token names "test_event_name", so that way the examples will only create/delete their own stuff.