weave --local status now reports plugin.
weave --local status now reports plugin.

Prints the following when running:
```
        Service: plugin
     DriverName: weave
```
See also:
- https://weaveworks.slack.com/archives/net/p1488563299009870
- https://weaveworks.slack.com/archives/net/p1488539841009756

weaveworks/weave,weaveworks/weave,weaveworks/weave,weaveworks/weave