Create an EQC statem test for the DVV style riak_object

When making test I had to cut and paste the `riak_kv_vnode:put_merge` into the test. The same code is also cut and pasted into `ec_eqc`. Seems an obvious candidate for a refactor. And `riak_object` seemed like the location since `put_merge` tinkered with `riak_object` state.