Return all endpoint data in order to prepare for new data format
Remove logic from fixture data
Move fixtures to where they belong
introduce new key cluster_replica_groups_for_cfn_stack

which returns a flattened array of all stacks' redis elasticache
clusters' replica groups

todo: refactor tests
beautifying
More refactoring
documentation
regression fix: do not touch `cluster_nodes_for_cfn_stack` method
fix: replication groups is no hash but an overloaded magic API method
be nice to code cop