Scope needs updating for Weave Net 2.0

[bboreham]

This code: https://github.com/weaveworks/scope/blob/master/probe/overlay/weave.go
It's attempting to talk to a weaveproxy container, which no longer exists.

[rade]

This is a problem already since in a CNI context the proxy won't be running. Nor will the plugin. Cue lots of log noise that terrifies users - see #2628.

[rade]

Would it be reasonable to simply remove the plugin and proxy stuff from that code?

[rade]

Actually, I guess we should obtain the info from the Weave Net 2.0 status json, since it's included there now. I don't think we should bother keeping the existing code for old Weave Net versions, especially since, as observed above, it can generate log noise there too. We should however make sure that the new status retrieval code can cope with an old version json.