Add Event Type and Instance ID to the event log

[markdryan]

The only information available in the event log right now is

Timestamp time.Time
TenantID  string
EventType string
Message   string

This is not really enough information to use these events programmatically. For example, in the BAT tests I'd like to delete and instance and wait for the instance delete event to arrive. The problem is that I currently have no way of knowing that the newly arrived event is

a) an instance deleted event and not some unrelated event generated by some other part of the cluster
b) pertains to the instance I deleted.

I'm entering this as a bug as the event log feature isn't really usable without these additional fields.