Add tests for SC byzantine dataloss and tree loss

This is the first iteration of creating byzantine dataloss tests that
show both recoverable and unrecoverable, but detectable errors. This tests the
following scenarios.

 * Lose one partition worth of data, but no synctrees and recover.
 * Lose all but one partition of ensemble data, but no synctrees and
   recover.
 * Lose minority of synctrees. Only the peers with the missing
   synctrees are restarted. System remains available.
 * Loss of majority of synctrees. Majority peers are restarted. System
   recovers when they all come back online.
 * Loss of majority of synctrees with one node partitioned. All peers
   restarted except partitioned one. System does not recover with that
   node partitioned. When the partition is healed the system recovers.
 * Loss of all data and synctree except on one peer recovers.
 * Backing up and restoring old data but not synctrees results in
   detected errors. Restoring newer data fixes this.
 * Delete all data on all nodes, but not synctrees. This is detected and
   an error returned to the user.
Use rt functions to safely remove backend data

Use riak_test_runner:metadata/0 to get the configured backend instead of
defaulting to bitcask. Additionally we use rt:clean_data_dir/2 to safely
remove backend directories.
WIP - Add ensemble_ring_changes

Ensemble_ring_changes tests writing a value, expanding the cluster, then
updating and reading that value after ring expansion has completed. It
also creates a bucket using a bucket type with a different n_val from
the default bucket type.  The latter tests basho/riak_kv#1008 and it's
corresponding riak_core PR.
Fixup ensemble_ring_changes

* Add some logging
* Ensure updates work before and after ring expansion
Update ensemble_ring_changes w/ node replace test

Additionally fix cluster expansion and make test deterministically pass.
add force_replace test to ensemble_ring_changes
Merge pull request #673 from basho/ajs/ensemble-ring-changes

Add ensemble_ring_changes
Merge pull request #666 from basho/ajs/ensemble_byzantine

Add tests for SC byzantine dataloss and tree loss