CBQE-867 fix the bug in data conversion test

Change-Id: If288f7f485019ce57d6290314d204c31226696ac
Reviewed-on: http://review.couchbase.org/27234
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>