Include weave exposed addresses in ps output

[awh]

Fixes #385. Sample output:

$ sudo ./weave ps
e8f979801cd7 ae:50:e8:95:f6:03 10.0.0.1/24
2e25b47b08fe 6a:95:45:20:14:56
weave 7a:c4:8b:a1:e6:ad 10.0.0.2/24

The final entry uses $BRIDGE in place of the container name, for lack of anything better - thoughts @rade @bboreham ?

[rade]

$BRIDGE is fine.

Docs?

[bboreham]

Doesn't "weave" clash with what you get from weave ps weave ?

[awh]

Doesn't "weave" clash with what you get from weave ps weave ?

Very much so - well spotted. Container names are restricted to these characters

https://github.com/ajhager/docker/blob/master/runtime.go#L35

though so the literal string weave:expose is neither a valid container name nor identifier, and is exactly twelve characters long so the output remains nicely formatted:

$ sudo ./weave ps
e8f979801cd7 ae:50:e8:95:f6:03 10.0.0.1/24
2e25b47b08fe 6a:95:45:20:14:56
weave:expose 7a:c4:8b:a1:e6:ad 10.0.0.2/24

[awh]

Amended the commit to use weave:expose, restore filtering and update documentation.