Increase ensemble tick from 200ms to 500ms
Increase ensemble tick from 200ms to 500ms

This commit slightly increases the ensemble tick rate in order to
decrease the commit frequency and reduce load when using a large
number of ensembles.

ricardobcl/riak_ensemble,cmeiklejohn/riak_ensemble,sargun/riak_ensemble,basho/riak_ensemble,ricardobcl/riak_ensemble,basho/riak_ensemble,sargun/riak_ensemble,cmeiklejohn/riak_ensemble