[SPARK-21718][SQL] Heavy log of type: "Skipping partition based on stats ..."

## What changes were proposed in this pull request?

Reduce 'Skipping partitions' message to debug

## How was this patch tested?

Existing tests

Author: Sean Owen <sowen@cloudera.com>

Closes #19010 from srowen/SPARK-21718.

sql/core/src/main/scala/org/apache/spark/sql/execution/columnar/InMemoryTableScanExec.scala

@@ -166,12 +166,13 @@ case class InMemoryTableScanExec(
         if (inMemoryPartitionPruningEnabled) {
           cachedBatchIterator.filter { cachedBatch =>
             if (!partitionFilter.eval(cachedBatch.stats)) {
-              def statsString: String = schemaIndex.map {
-                case (a, i) =>
+              logDebug {
+                val statsString = schemaIndex.map { case (a, i) =>
                   val value = cachedBatch.stats.get(i, a.dataType)
                   s"${a.name}: $value"
-              }.mkString(", ")
-              logInfo(s"Skipping partition based on stats $statsString")
+                }.mkString(", ")
+                s"Skipping partition based on stats $statsString"
+              }
               false
             } else {
               true