[SPARK-26564] Fix misleading error message about spark.network.timeout and spark.executor.heartbeatInterval

If users set equivalent values to spark.network.timeout and spark.executor.heartbeatInterval, they get the following message:

```
java.lang.IllegalArgumentException: requirement failed: The value of spark.network.timeout=120s must be no less than the value of spark.executor.heartbeatInterval=120s.
```

But it's misleading since it can be read as they could be equal. So this fix replaces "no less than" with "greater than".

Author: sekikn

core/src/main/scala/org/apache/spark/SparkConf.scala

@@ -619,7 +619,7 @@ class SparkConf(loadDefaults: Boolean) extends Cloneable with Logging with Seria
     // If spark.executor.heartbeatInterval bigger than spark.network.timeout,
     // it will almost always cause ExecutorLostFailure. See SPARK-22754.
     require(executorTimeoutThresholdMs > executorHeartbeatIntervalMs, "The value of " +
-      s"spark.network.timeout=${executorTimeoutThresholdMs}ms must be no less than the value of " +
+      s"spark.network.timeout=${executorTimeoutThresholdMs}ms must be greater than the value of " +
       s"spark.executor.heartbeatInterval=${executorHeartbeatIntervalMs}ms.")
   }