AtomicFileWriter.commit should use Util.deleteFile so as to get a more...

AtomicFileWriter.commit should use Util.deleteFile so as to get a more meaningful error message in case the deletion fails.
The following is not helpful in terms of diagnosing the root problem:
java.io.IOException: Unable to delete /…/jobs/demo/builds/…/workflow/3.xml
	at hudson.util.AtomicFileWriter.commit(AtomicFileWriter.java:112)
	at hudson.XmlFile.write(XmlFile.java:179)
	at org.jenkinsci.plugins.workflow.support.storage.SimpleXStreamFlowNodeStorage.saveActions(SimpleXStreamFlowNodeStorage.java:106)
	at …

core/src/main/java/hudson/util/AtomicFileWriter.java

@@ -23,6 +23,7 @@
  */
 package hudson.util;
 
+import hudson.Util;
 import java.io.BufferedWriter;
 import java.io.File;
 import java.io.FileOutputStream;
@@ -107,9 +108,13 @@ public class AtomicFileWriter extends Writer {
 
     public void commit() throws IOException {
         close();
-        if(destFile.exists() && !destFile.delete()) {
-            tmpFile.delete();
-            throw new IOException("Unable to delete "+destFile);
+        if (destFile.exists()) {
+            try {
+                Util.deleteFile(destFile);
+            } catch (IOException x) {
+                tmpFile.delete();
+                throw x;
+            }
         }
         tmpFile.renameTo(destFile);
     }