add with_each_shard for rails 3 relations

Change-Id: Ic907525d7ff1a1d3db927de3453475ff972ff516
Reviewed-on: https://gerrit.instructure.com/27540
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>

config/initializers/active_record.rb

@@ -976,6 +976,14 @@ unless CANVAS_RAILS2
     end
     alias_method_chain :delete_all, :limit
   end
+
+  def with_each_shard
+    if block_given?
+      Array(yield(self))
+    else
+      self.to_a
+    end
+  end
 end
 
 ActiveRecord::ConnectionAdapters::AbstractAdapter.class_eval do