Wire in NodeExtraConfig interface

Wire in NodeExtraConfig interface

It's become apparent that some actions are required in the pre-deploy
phase for all nodes, for example applying common hieradata overrides,
or also as a place to hook in logic which must happen for all nodes
prior to their removal on scale down (such as unregistration from
a satellite server, which currently doesn't work via the
*NodesPostDeployment for scale-down usage).

So, add a new interface that enables ExtraConfig per-node (inside the
scaled unit, vs AllNodes which is used for the cluster-wide config
outside of the ResourceGroup)

Change-Id: Ic865908e97483753e58bc18e360ebe50557ab93c