[SPARK-22357][CORE] SparkContext.binaryFiles ignore minPartitions parameter

## What changes were proposed in this pull request?
Fix the issue that minPartitions was not used in the method. This is a simple fix and I am not trying to make it complicated. The purpose is to still allow user to control the defaultParallelism through the value of minPartitions, while also via sc.defaultParallelism parameters.

## How was this patch tested?
I have not provided the additional test since the fix is very straightforward.

Closes apache#21638 from bomeng/22357.

Lead-authored-by: Bo Meng <[email protected]>
Co-authored-by: Bo Meng <[email protected]>
Signed-off-by: Sean Owen <[email protected]>

Author: 2 people

core/src/main/scala/org/apache/spark/input/PortableDataStream.scala

@@ -47,7 +47,7 @@ private[spark] abstract class StreamFileInputFormat[T]
   def setMinPartitions(sc: SparkContext, context: JobContext, minPartitions: Int) {
     val defaultMaxSplitBytes = sc.getConf.get(config.FILES_MAX_PARTITION_BYTES)
     val openCostInBytes = sc.getConf.get(config.FILES_OPEN_COST_IN_BYTES)
-    val defaultParallelism = sc.defaultParallelism
+    val defaultParallelism = Math.max(sc.defaultParallelism, minPartitions)
     val files = listStatus(context).asScala
     val totalBytes = files.filterNot(_.isDirectory).map(_.getLen + openCostInBytes).sum
     val bytesPerCore = totalBytes / defaultParallelism