used enquoteIdentifier to escape quotes in cluster name

Author: chernser

jdbc-v2/src/main/java/com/clickhouse/jdbc/ConnectionImpl.java

@@ -76,7 +76,7 @@ public ConnectionImpl(String url, Properties info) throws SQLException {
             this.config = new JdbcConfiguration(url, info);
             final String tmpClusterName = config.getDriverProperty(DriverProperties.CLUSTER_NAME.getKey(), DriverProperties.CLUSTER_NAME.getDefaultValue());
             this.cluster = tmpClusterName == null ? null : tmpClusterName.trim();
-            this.onCluster = this.cluster != null && !this.cluster.trim().isEmpty();
+            this.onCluster = this.cluster != null && !this.cluster.isEmpty();
             this.appName = "";
             this.readOnly = false;
             this.holdability = ResultSet.HOLD_CURSORS_OVER_COMMIT;

jdbc-v2/src/main/java/com/clickhouse/jdbc/StatementImpl.java

@@ -334,7 +334,7 @@ public void cancel() throws SQLException {
         }
 
         try (QueryResponse response = connection.getClient().query(String.format("KILL QUERY%sWHERE query_id = '%s'",
-                connection.onCluster ? " ON CLUSTER `" + connection.cluster + "` " : " ",
+                connection.onCluster ? " ON CLUSTER " + SQLUtils.enquoteIdentifier(connection.cluster, true) + ' ' : ' ',
                 lastQueryId), connection.getDefaultQuerySettings()).get()){
             LOG.debug("Query {} was killed by {}", lastQueryId, response.getQueryId());
         } catch (Exception e) {