[COOK-1318] - Create a to_ary method that returns nil

When loading the resource collection in shef, (and possibly elsewhere), the
find method used by resources() in the recipe DSL attempts to find an
application_to_ary resource, instead of application in method_missing.

resources/default.rb

@@ -117,3 +117,8 @@ def method_missing(name, *args, &block)
   @sub_resources << resource
   resource
 end
+
+def to_ary
+  nil
+end
+alias :to_a :to_ary