Add include_for_find support via 'expand'

Allows for opt in of `:include_for_find` option for `Rbac::Filterer` via
the `expand` request parameter.

Include for find will effectively add a `.include` to the base query
done in `collection_search`, which in cases like this:

    /api/vms?expand=resources,hardware&attributes=num_cpu,name

Can avoid an N+1 on the associated resource.

Author: NickLaMuro

app/controllers/api/base_controller/parameters.rb

@@ -100,6 +100,16 @@ def sort_directive(klass, attr, order, options)
         end
         arel
       end
+
+      def determine_include_for_find(klass)
+        return nil unless klass.respond_to?(:reflect_on_association)
+
+        relations = @req.derived_include_for_find.select do |relation|
+                      klass.reflect_on_association(relation)
+                    end
+
+        relations.empty? ? nil : relations
+      end
     end
   end
 end

app/controllers/api/base_controller/renderer.rb

@@ -185,6 +185,7 @@ def collection_filterer(res, type, klass, is_subcollection = false)
         options[:filter] = miq_expression if miq_expression
         options[:offset] = params['offset'] if params['offset']
         options[:limit] = params['limit'] if params['limit']
+        options[:include_for_find] = determine_include_for_find(klass)
 
         filter_results(miq_expression, res, options)
       end

lib/api/request_adapter.rb

@@ -37,6 +37,10 @@ def attributes
       @attributes ||= @params['attributes'].to_s.split(',')
     end
 
+    def derived_include_for_find
+      @derived_include_for_find ||= expand_requested.reject { |item| item == "resource" }
+    end
+
     def base
       url.partition(fullpath)[0] # http://target
     end