Riak 2.0 adoption

This will be the first pull request to adapt to Riak 2.0. To run this test:

- update `riak_test` to the latest branch, from `riak-1.4` branch
- add `sasl` to `incl_apps` of `riak_test`
- update `.riak_test.config` as

```erlang
     {build_paths, [{root,              "/home/kuenishi/rt/riak"},
                    {current,           "/home/kuenishi/rt/riak/current"},
                    {ee_root,           "/home/kuenishi/rt/riak_ee"},
                    {ee_current,        "/home/kuenishi/rt/riak_ee/current"},
                    {ee_previous,       "/home/kuenishi/rt/riak_ee_onefour/current"},
                    {cs_root,           "/home/kuenishi/rt/riak_cs"},
                    {cs_current,        "/home/kuenishi/rt/riak_cs/current"},
                    {cs_previous,        "/home/kuenishi/rt/riak_cs/1.5.0"},
                    {stanchion_root,    "/home/kuenishi/rt/stanchion"},
                    {stanchion_current, "/home/kuenishi/rt/stanchion/current"},
                    {stanchion_previous,       "/home/kuenishi/rt/stanchion/1.5.0"}
                   ]},
```

Many things left to do:

- merge `release/1.5` branch after 1.5.1 release
- `repl_v3_test` and `repl_test` still does not work with riak-ee-2.0
- discuss on deprecation of v2 replication
- migration tests
- introduce cuttlefish