TreeBuilder: calculate active_node at render time.
TreeBuilder: calculate active_node at render time.

The builder class is sometimes built early in the controller logic and
the active tree node is set later on. So for the view partial we need
the render-time current value for the select_node key.
(transferred from ManageIQ/manageiq@c64caf9e567508e537d5a4cb75fc330ca82dd00f)

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic