WIP: Add EQC riak_test for cluster metadata broadcast

Combine the broadcast_eqc test developed by Quviq with riak_test that exercises broadcast of cluster-metadata using statem. 

- Cluster set up is done in a property, so cluster sizes are varied
- Make use of intercepts to send messages to the cluster_meta_proxy_server. Add support for "bursty" message sending from the proxy to the cluster nodes.

Note: this test currently fails occasionally because consistency problems that may be related to a known bug. As the test is written now, the exchange and lazy timers are set to max values, so there should be no tree healing, which causes the issue to be exhibited. [1]

1. https://github.com/basho/riak_core/issues/378

Issue: https://github.com/basho/riak_core/issues/373