[AWS|DynamoDB] update item should not be idempotent when an action is specified

lib/fog/aws/requests/dynamodb/update_item.rb

@@ -37,10 +37,12 @@ module Fog
             'TableName'         => table_name
           }.merge(options)
 
+          idempotent = attribute_updates.any? {|key, value| value.has_key?('Action')}
+
           request(
             :body       => MultiJson.encode(body),
             :headers    => {'x-amz-target' => 'DynamoDB_20111205.UpdateItem'},
-            :idempotent => true
+            :idempotent => idempotent
           )
         end