[FIXED JENKINS-9540] Failure of recursive copy on slave side should be reported.

Instead it was being thrown in a Future that the master did not wait for:
the writing side failed with a closed pipe exception, and this meaningless error was thrown up.
Fixing by waiting for the reading side first, so any error there will be thrown up.
(If there was _also_ an error on the writing side, we would miss it, but typically this will just be the closed stream.)

core/src/test/java/hudson/FilePathTest.java

@@ -206,6 +206,46 @@ public class FilePathTest extends ChannelTestCase {
         }
     }
 
+    @Bug(9540)
+    public void testErrorMessageInRemoteCopyRecursive() throws Exception {
+        File tmp = Util.createTempDir();
+        try {
+            File src = new File(tmp, "src");
+            File dst = new File(tmp, "dst");
+            FilePath from = new FilePath(src);
+            FilePath to = new FilePath(british, dst.getAbsolutePath());
+            for (int i = 0; i < 10000; i++) {
+                // TODO is there a simpler way to force the TarOutputStream to be flushed and the reader to start?
+                // Have not found a way to make the failure guaranteed.
+                OutputStream os = from.child("content" + i).write();
+                try {
+                    for (int j = 0; j < 1024; j++) {
+                        os.write('.');
+                    }
+                } finally {
+                    os.close();
+                }
+            }
+            FilePath toF = to.child("content0");
+            toF.write().close();
+            toF.chmod(0400);
+            try {
+                from.copyRecursiveTo(to);
+                // on Windows this may just succeed; OK, test did not prove anything then
+            } catch (IOException x) {
+                if (Functions.printThrowable(x).contains("content0")) {
+                    // Fine, error message talks about permission denied.
+                } else {
+                    throw x;
+                }
+            } finally {
+                toF.chmod(700);
+            }
+        } finally {
+            Util.deleteRecursive(tmp);
+        }
+    }
+
     public void testArchiveBug4039() throws Exception {
         File tmp = Util.createTempDir();
         try {