allow AR::Base objects in Shard.*_id_for stubs

test-plan:
 - specs pass

Change-Id: I6fd8e53fe9c22a00fdf74f6a9860b0adbda0018d
Reviewed-on: https://gerrit.instructure.com/22546
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Jacob Fugal <jacob@instructure.com>
QA-Review: Jacob Fugal <jacob@instructure.com>

Author: lukfugl

lib/stubs/shard.rb

@@ -67,11 +67,11 @@ def relative_id_for(any_id, target_shard = nil)
   end
 
   def self.global_id_for(any_id)
-    any_id
+    any_id.is_a?(ActiveRecord::Base) ? any_id.global_id : any_id
   end
 
   def self.relative_id_for(any_id, target_shard = nil)
-    any_id
+    any_id.is_a?(ActiveRecord::Base) ? any_id.local_id : any_id
   end
 
   yaml_as "tag:instructure.com,2012:Shard"