[SPARK-15158][CORE] downgrade shouldRollover message to debug level

## What changes were proposed in this pull request?
set log level to debug when check shouldRollover

## How was this patch tested?
It's tested manually.

Author: depend <depend@gmail.com>

Closes #12931 from depend/master.

core/src/main/scala/org/apache/spark/util/logging/RollingPolicy.scala

@@ -113,7 +113,7 @@ private[spark] class SizeBasedRollingPolicy(
 
   /** Should rollover if the next set of bytes is going to exceed the size limit */
   def shouldRollover(bytesToBeWritten: Long): Boolean = {
-    logInfo(s"$bytesToBeWritten + $bytesWrittenSinceRollover > $rolloverSizeBytes")
+    logDebug(s"$bytesToBeWritten + $bytesWrittenSinceRollover > $rolloverSizeBytes")
     bytesToBeWritten + bytesWrittenSinceRollover > rolloverSizeBytes
   }