Changes to fix a broken CRDT map (see riak_dt#82) break this test

Well, that's not true. They break riak_kv's context operations on Maps.
This change works around that breakage by turning the context off for
the operations in this test. It is a temporary thing, when the context fix
work has been done, we'll be changing back.
Merge pull request #550 from basho/rdb/workaround-broken-ctx

Changes to fix a broken CRDT map (see riak_dt#82) break this test