Makes Payload a type with FilterByKey so that Payloads can implement
filtering by key. With this approach we don't need to expose a Namespace
field on Event, and we don't need to invest micro formats or require a
bunch of code to be aware of exactly how the key field is encoded.
The subscribe endpoint needs to be able to inspect the payload to filter
events, and convert them into the protobuf types.
Use the protobuf CatalogOp type for the operation field, for now. In the
future if we end up with multiple interfaces we should be able to remove
the protobuf dependency by changing this to an int32 and adding a test
for the mapping between the values.
Make the value of the payload a concrete type instead of interface{}. We
can create other payloads for other event types.
The nodeCheck slice was being used as the first arg in append, which in some cases will modify the array backing the slice. This would lead to service checks for other services in the wrong event.
Also refactor some things to reduce the arguments to functions.
Daniel Nephin