integration: use NTS by default

By default, the tests used SimpleStrategy if there was a single DC.
Using SimpleStrategy is discouraged. Apart from that, Scylla seems to
disable the tablets by default for SimpleStrategy keyspaces - we want
to prevent that.

For Cassandra, we still will be using SimpleStrategy.

Author: muzarski

tests/src/integration/integration.cpp

@@ -268,7 +268,9 @@ std::string Integration::default_replication_strategy() {
     replication_strategy_s << "'NetworkTopologyStrategy', 'dc1': " << number_dc1_nodes_ << ", "
                            << "'dc2': " << number_dc2_nodes_;
   } else {
-    replication_strategy_s << "'SimpleStrategy', 'replication_factor': ";
+    // Currently we use Cassandra 3.11.19, which disallows the use of `replication_factor` with NTS.
+    std::string strategy = Options::is_scylla() ? "'NetworkTopologyStrategy'" : "'SimpleStrategy'";
+    replication_strategy_s << strategy << ", 'replication_factor': ";
 
     // Ensure the replication factor has not been overridden or already set
     if (replication_factor_ == 0) {