Fix BasicLoadBalancingPolicy.getReplica empty partitioner (#503)

Queries getting paritioner set either from user, or when statement is
being built against cdc tablet.
In other cases statement does not get any partitioner.
For proper tablet routing driver needs to calculate token from the key,
which needs partitioner, if partitioner is not present driver returns empty replica list.

This fix is rather quick-fix.
Implementing proper solution that will help with CDC+tablets case, is
scheduled at #502

Author: dkropachev

core/src/main/java/com/datastax/oss/driver/api/core/metadata/TokenMap.java

@@ -189,4 +189,8 @@ default Set<Node> getReplicas(@NonNull String keyspaceName, @NonNull TokenRange
   /** The name of the partitioner class in use, as reported by the Cassandra nodes. */
   @NonNull
   String getPartitionerName();
+
+  /** The partitioner class in use, as reported by the Cassandra nodes. */
+  @NonNull
+  Partitioner getPartitioner();
 }

core/src/main/java/com/datastax/oss/driver/internal/core/loadbalancing/BasicLoadBalancingPolicy.java

@@ -333,6 +333,9 @@ protected Set<Node> getReplicas(@Nullable Request request, @Nullable Session ses
       }
 
       partitioner = request.getPartitioner();
+      if (partitioner == null && maybeTokenMap.isPresent()) {
+        partitioner = maybeTokenMap.get().getPartitioner();
+      }
     } catch (Exception e) {
       // Protect against poorly-implemented Request instances
       LOG.error("Unexpected error while trying to compute query plan", e);

core/src/main/java/com/datastax/oss/driver/internal/core/metadata/token/DefaultTokenMap.java

@@ -207,6 +207,12 @@ public String getPartitionerName() {
     return tokenFactory.getPartitionerName();
   }
 
+  @NonNull
+  @Override
+  public Partitioner getPartitioner() {
+    return tokenFactory;
+  }
+
   private KeyspaceTokenMap getKeyspaceMap(CqlIdentifier keyspace) {
     Map<String, String> config = replicationConfigs.get(keyspace);
     return (config == null) ? null : keyspaceMaps.get(config);