[CORE] [MINOR] change the log level to info

Too many logs even when set the log level to warning.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #7340 from chenghao-intel/log and squashes the following commits:

59658cf [Cheng Hao] change the log level to info

core/src/main/scala/org/apache/spark/executor/Executor.scala

@@ -443,7 +443,7 @@ private[spark] class Executor(
     try {
       val response = heartbeatReceiverRef.askWithRetry[HeartbeatResponse](message)
       if (response.reregisterBlockManager) {
-        logWarning("Told to re-register on heartbeat")
+        logInfo("Told to re-register on heartbeat")
         env.blockManager.reregister()
       }
     } catch {