Allow extending resources state

[invidian]

Currently resource state is simply a containers state, but there are things, which are part of the state beyond just containers, like list of etcd users, roles etc. Kubelet node roles, annotations etc, which should also be stored, so diff can be provided to the user if something needs to be updated.

Note: not all resources may require it, but perhaps it will make sense to have some interface for getting containers state for example.