Improvements to Cluster Metadata Tests

The changes to `cluster_meta_basic` increase some coverage of this sanity check test. `cluster_meta_rmr` is a test not destined for a giddyup suite but I think is useful to have in the develop branch. It can be run against a `riak_core` cluster to measure certain properties of cluster meta. It is admittedly a bit impractical for some to run, because any useful measurements require at least 10 to 40 nodes. To make sure it is runnable, i have commented out the requirement of such a high node-count and instead defaulted it to use the standard five node devrel so a reviewer can try and run it. In addition, running this test at higher node counts requires working around the `nothing_planned` issue. No workaround for that issue provided as part of this PR. 

The changes to `cluster_meta_basic` require https://github.com/basho/riak_core/pull/457

Partially addresses https://github.com/basho/riak_core/issues/373