TS-938 - Don't merge

Adding the config and a gen_server to handle the c* nodes. But this uses elysium 0.1.7 so the files changed are really misleading.

Also the query seems to work, but it is not currently being used.
-- doesn't account for duplicates. Better bet would be to use ordsets:from_list and ordsets:subtract. I think we want each node to only occur once even if the nodes query somehow returns a node duplicated. And the nodes should probably be converted to cassandra_node() before constructing an ordset to remain compatible with the existing logic that expects {Host, Port}.