Log case when toCreate is 0 to investigate reason

We assuming that in some cases toCreate ends up in 0.
In order to investigate it we need a plug to log it and show original
data.

Author: dkropachev

driver-core/src/main/java/com/datastax/driver/core/HostConnectionPool.java

@@ -300,6 +300,15 @@ ListenableFuture<Void> initAsyncWithConnection(Connection reusedConnection) {
         maxConnections / shardsCount + (maxConnections % shardsCount > 0 ? 1 : 0);
     int toCreate = shardsCount * connectionsPerShard;
 
+    if (toCreate == 0) {
+      logger.error(
+          "Initializing connection, reusing old one when toCreate = {}, shardsCount = {}, coreSize = {}, hostDistance = {}",
+          toCreate,
+          shardsCount,
+          coreSize,
+          hostDistance);
+    }
+
     this.connections = new List[shardsCount];
     scheduledForCreation = new AtomicInteger[shardsCount];
     open = new AtomicInteger[shardsCount];