Consider datatype while creating item instance

- UprConsumer::mutation

Change-Id: Iec6e4c2f95728e740781cacaf13a5a14732cb564
Reviewed-on: http://review.couchbase.org/33895
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>