Allow listing of resources and nested resources

This allows the engine to optionally include resources from nested
stacks in a resource-list up to `depth` levels below.  This number is
limited by `max_nested_stack_depth`.

Implements: blueprint explode-nested-resources
Change-Id: I43a5af25e74c7bfb32260f1616d36b311e0f2631
Merge "Allow listing of resources and nested resources"