[SPARK-18960][SQL][SS] Avoid double reading file which is being copied.

## What changes were proposed in this pull request?

In HDFS, when we copy a file into target directory, there will a temporary `._COPY_` file for a period of time. The duration depends on file size. If we do not skip this file, we will may read the same data for two times.

## How was this patch tested?
update unit test

Author: uncleGen <hustyugm@gmail.com>

Closes #16370 from uncleGen/SPARK-18960.

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/PartitioningAwareFileIndex.scala

@@ -439,10 +439,15 @@ object PartitioningAwareFileIndex extends Logging {
 
   /** Checks if we should filter out this path name. */
   def shouldFilterOut(pathName: String): Boolean = {
-    // We filter everything that starts with _ and ., except _common_metadata and _metadata
+    // We filter follow paths:
+    // 1. everything that starts with _ and ., except _common_metadata and _metadata
     // because Parquet needs to find those metadata files from leaf files returned by this method.
     // We should refactor this logic to not mix metadata files with data files.
-    ((pathName.startsWith("_") && !pathName.contains("=")) || pathName.startsWith(".")) &&
-      !pathName.startsWith("_common_metadata") && !pathName.startsWith("_metadata")
+    // 2. everything that ends with `._COPYING_`, because this is a intermediate state of file. we
+    // should skip this file in case of double reading.
+    val exclude = (pathName.startsWith("_") && !pathName.contains("=")) ||
+      pathName.startsWith(".") || pathName.endsWith("._COPYING_")
+    val include = pathName.startsWith("_common_metadata") || pathName.startsWith("_metadata")
+    exclude && !include
   }
 }

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/FileIndexSuite.scala

@@ -142,6 +142,7 @@ class FileIndexSuite extends SharedSQLContext {
     assert(!PartitioningAwareFileIndex.shouldFilterOut("_common_metadata"))
     assert(PartitioningAwareFileIndex.shouldFilterOut("_ab_metadata"))
     assert(PartitioningAwareFileIndex.shouldFilterOut("_cd_common_metadata"))
+    assert(PartitioningAwareFileIndex.shouldFilterOut("a._COPYING_"))
   }
 
   test("SPARK-17613 - PartitioningAwareFileIndex: base path w/o '/' at end") {