Allow CNI caller to supply blank netns; upgrade cni library to version 0.5.0

[bboreham]

Prompted by the impending release of Kubernetes 1.6, which seems to rely on the behaviour that a blank netns is allowed on DEL.

Lots of lines changed, because the CNI return format changed. The library should take care of returning backwards-compatible results to older runtimes.

[jbeda]

I think one problem is that there is no cniVersion member in the weave configuration:

cat /etc/cni/net.d/10-weave.conf
{
    "name": "weave",
    "type": "weave-net"
}

I suspect (no confirmation) that the runtime then assumes the latest version. It might be that setting "cniVersion": "0.2.0" there fixes things.

[bboreham]

That's an interesting idea, but the CNI spec says that an absence of version shall be interpreted as version 0.1, and the currently-released Weave Net plugin is at CNI spec level 0.1.

As discussed on sig-network Slack, kubelet needs to be prepared for the DEL to error, and move on past that operation at some point.

[luxas]

I can confirm that this fixes the weave-kube problem with v1.6.
However, we should bump the version of weave-plugin so the new plugin binary will be used; when I tested this I had to manually remove the current weave CNI plugin binary in order to get the new one deployed

[bboreham]

Thanks @luxas; we will make a new release soon which will have a higher version number.

[luxas]

Was this merged into master as well?
Is there any reason to not fix this on master as well?
I'd like to be able to use the CI-built (:latest) version to actually test it out and make sure it's working from official builds

[bboreham]

@luxas merged to master now; sorry for oversight

However the CI build flaked first time