raft: replication_test: extract tickers initialization into a separate func
raft: replication_test: extract tickers initialization into a separate func

Extract raft tickers initialization into `init_raft_tickers()`
functon. This will be later used in rpc tests.

Signed-off-by: Pavel Solodovnikov <2cf5887fafb117b7ff3e29b9720a7305c3313494@scylladb.com>

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