added cpu arithmetic operations tests
added cpu arithmetic operations tests

apache/incubator-singa,apache/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa,apache/incubator-singa