alternator-test: add batch writing test case
alternator-test: add batch writing test case

Message-Id: <acbb918e3115e5d0bff17694f997c289b3dea2f9@scylladb.com>

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