raft: replication test: move declarations up
raft: replication test: move declarations up

Move declarations near the top of the file for following refactors to
raft_cluster.

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

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