Issue #12451: Add support.create_empty_file()

We don't need to create a temporary buffered binary or text file object just to
create an empty file.

Replace also os.fdopen(handle).close() by os.close(handle).
diff --git a/Lib/test/test_zipimport.py b/Lib/test/test_zipimport.py
index ab669cf..56141ef 100644
--- a/Lib/test/test_zipimport.py
+++ b/Lib/test/test_zipimport.py
@@ -411,7 +411,7 @@
 
     def testEmptyFile(self):
         support.unlink(TESTMOD)
-        open(TESTMOD, 'w+').close()
+        support.create_empty_file(TESTMOD)
         self.assertZipFailure(TESTMOD)
 
     def testFileUnreadable(self):