Fix flaky tests on Travis

Line 87-88 in `helpers/match_helper.py` was the culprit; `event = Event` should have been `event = Event()`.

The reason for the hackish code on those two lines was because Match.renderKeyName() took in an `event` rather than an `event_key_name`.

This is different from all of the other renderKeyNames we have (the others have arguments as strings or ints, not models), so I changed it to take in `event_key_name`. This resulted in changes everywhere this method is called; every instance of `Match.renderKeyName(event, ...)` got changed to `Match.renderKeyName(event.key.id())`.