raft: replication test: use Seastar random generator
raft: replication test: use Seastar random generator

Use the random generator provided by Seastar test suite.

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

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