Revert "Avoid full cluster scans in Connection.checkClusterName (#1195)"

This reverts commit 60e6696.

Author: Alexandre Dutra

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

@@ -382,9 +382,7 @@ private ListenableFuture<Void> checkClusterName(
 
     DefaultResultSetFuture clusterNameFuture =
         new DefaultResultSetFuture(
-            null,
-            protocolVersion,
-            new Requests.Query("select cluster_name from system.local where key = 'local'"));
+            null, protocolVersion, new Requests.Query("select cluster_name from system.local"));
     try {
       write(clusterNameFuture);
       return GuavaCompatibility.INSTANCE.transformAsync(