The PluginManager almost duplicates the network plugin interface, but
not quite since the Init() function should be called by whatever
actually finds and creates the network plugin instance. Only then
does it get passed off to the PluginManager.
The Manager synchronizes pod-specific network operations like setup,
teardown, and pod network status. It passes through all other
operations so that runtimes don't have to cache the network plugin
directly, but can use the PluginManager as a wrapper.
