Add tests for amendment log, and a bit code reformat

RIAK-1212

- Add a function `riak_cs_access:flush_to_log/2,3` which outputs one access key and value supposed to be put into `moss.access`.
- `flush_to_log/2` folds around all ets entries and outputs all of them to each line, with JSON encoded
- `flush_to_log/3` outputs single key and value to log.
- The test works as follows:
 - write some data to CS
 - kill all Riak process
 - try to flush the access stats
 - check Riak CS log and verifies whether correct log is updated or not.