Updates the spec and plugins to return an array of interfaces and IP details
to the runtime including:
- interface names and MAC addresses configured by the plugin
- whether the interfaces are sandboxed (container/VM) or host (bridge, veth, etc)
- multiple IP addresses configured by IPAM and which interface they
have been assigned to
Returning interface details is useful for runtimes, as well as allowing
more flexible chaining of CNI plugins themselves. For example, some
meta plugins may need to know the host-side interface to be able to
apply firewall or traffic shaping rules to the container.
Previously, the log lines appeared in stdout before the JSON encoding of
the error message. That would break JSON parsing of stdout. Instead, we use
stderr for these unstructured logs, consistent with the CNI spec.
This is an attempt to testing the PluginMain() function of the skel pkg.
We should be able to do better by using a mockable interface for the
plugins, but this is a start.
