In the course of setting out to add filters and address some cleanup, it
was found that we had a few problems in the events subsystem that needed
addressing before moving forward.
The biggest change was to move to the more standard terminology of
publish and subscribe. We make this terminology change across the Go
interface and the GRPC API, making the behavior more familier. The
previous system was very context-oriented, which is no longer required.
With this, we've removed a large amount of dead and unneeded code. Event
transactions, context storage and the concept of `Poster` is gone. This
has been replaced in most places with a `Publisher`, which matches the
actual usage throughout the codebase, removing the need for helpers.
There are still some questions around the way events are handled in the
shim. Right now, we've preserved some of the existing bugs which may
require more extensive changes to resolve correctly.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
a615a6fe5d