ProxyStepHandler/Controller need to check access before attempting to read information

This affects things like recursive :read-resource(-description) :read-children-resources and so on. The problem as it stands is that if you have, say, a host scoped role scoped to host=master, and there is also a slave host controller, and you try to :read-resource(recursive=true,proxies=true), the master will list the slave host controller in its list of child addresses. It will then execute /host=slave:read-resource(recursive=true,proxies=true), which will fail and roll back the tx since the master host scoped role does not have access to that resource.