This change further plumbs the components required for implementing
event filters. Specifically, we now have the ability to filter on the
`topic` and `namespace`.
In the course of implementing this functionality, it was found that
there were mismatches in the events API that created extra serialization
round trips. A modification to `typeurl.MarshalAny` and a clear
separation between publishing and forwarding allow us to avoid these
serialization issues.
Unfortunately, this has required a few tweaks to the GRPC API, so this
is a breaking change. `Publish` and `Forward` have been clearly separated in
the GRPC API. `Publish` honors the contextual namespace and performs
timestamping while `Forward` simply validates and forwards. The behavior
of `Subscribe` is to propagate events for all namespaces unless
specifically filtered (and hence the relation to this particular change.
The following is an example of using filters to monitor the task events
generated while running the [bucketbench tool](https://github.com/estesp/bucketbench):
```
$ ctr events 'topic~=/tasks/.+,namespace==bb'
...
2017-07-28 22:19:51.78944874 +0000 UTC bb /tasks/start {"container_id":"bb-ctr-6-8","pid":25889}
2017-07-28 22:19:51.791893688 +0000 UTC bb /tasks/start {"container_id":"bb-ctr-4-8","pid":25882}
2017-07-28 22:19:51.792608389 +0000 UTC bb /tasks/start {"container_id":"bb-ctr-2-9","pid":25860}
2017-07-28 22:19:51.793035217 +0000 UTC bb /tasks/start {"container_id":"bb-ctr-5-6","pid":25869}
2017-07-28 22:19:51.802659622 +0000 UTC bb /tasks/start {"container_id":"bb-ctr-0-7","pid":25877}
2017-07-28 22:19:51.805192898 +0000 UTC bb /tasks/start {"container_id":"bb-ctr-3-6","pid":25856}
2017-07-28 22:19:51.832374931 +0000 UTC bb /tasks/exit {"container_id":"bb-ctr-8-6","id":"bb-ctr-8-6","pid":25864,"exited_at":"2017-07-28T22:19:51.832013043Z"}
2017-07-28 22:19:51.84001249 +0000 UTC bb /tasks/exit {"container_id":"bb-ctr-2-9","id":"bb-ctr-2-9","pid":25860,"exited_at":"2017-07-28T22:19:51.839717714Z"}
2017-07-28 22:19:51.840272635 +0000 UTC bb /tasks/exit {"container_id":"bb-ctr-7-6","id":"bb-ctr-7-6","pid":25855,"exited_at":"2017-07-28T22:19:51.839796335Z"}
...
```
In addition to the events changes, we now display the namespace origin
of the event in the cli tool.
This will be followed by a PR to add individual field filtering for the
events API for each event type.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
af2d7f0e55