raft: replication test: cluster class
raft: replication test: cluster class

Use raft_cluster class to handle servers.

First part of this change.

Signed-off-by: Alejo Sanchez <004be06a28e38b437b038f9b5c0b9f5758b792e9@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla