Eqc-fsm version of listkeys statem test

Introduce an eqc-fsm version of the verify-listkeys-eqc statem test for comparison. Compare to that version here:
https://github.com/basho/riak_test/pull/372

As @kellymclaughlin comments in PR 372, there are still some items that should be considered for both versions:

- Once a cluster is created, bring nodes up and down and verify the listkeys results hold as long as a enough nodes remain up to satisfy the request.
- Change the test to load and test more than one bucket per cluster setup. The test must be changed to keep track of buckets that have been created and make the state tracking more complex, but this will provide more actual testing per cluster setup.
- There is no bucket list testing in this test. It seems more appropriate to create a separate test and property for that.