alternator: move to NetworkTopologyStrategy
alternator: move to NetworkTopologyStrategy

Imstead of SimpleStrategy, NetworkTopologyStrategy is used
for setting up the replication configuration for alternator tables.
Replication factor 3 is used along with a local datacenter,
unless alternator discovers that it's running on a test cluster with
less than 3 nodes - then, RF is reduced accordingly and emits a warning,
which was also the case for SimpleStrategy.

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