bpo-31904: skip some tests related to fifo on VxWorks (GH-23473)



On VxWork RTOS, FIFO must be created under directory "/fifos/". Some test cases related to fifo is invalid on VxWorks. So skip them.
diff --git a/Lib/test/test_shutil.py b/Lib/test/test_shutil.py
index 890f2c7..df7fbed 100644
--- a/Lib/test/test_shutil.py
+++ b/Lib/test/test_shutil.py
@@ -683,6 +683,8 @@ def custom_cpfun(a, b):
     # Issue #3002: copyfile and copytree block indefinitely on named pipes
     @unittest.skipUnless(hasattr(os, "mkfifo"), 'requires os.mkfifo()')
     @os_helper.skip_unless_symlink
+    @unittest.skipIf(sys.platform == "vxworks",
+                    "fifo requires special path on VxWorks")
     def test_copytree_named_pipe(self):
         os.mkdir(TESTFN)
         try:
@@ -1206,6 +1208,8 @@ def test_dont_copy_file_onto_symlink_to_itself(self):
 
     # Issue #3002: copyfile and copytree block indefinitely on named pipes
     @unittest.skipUnless(hasattr(os, "mkfifo"), 'requires os.mkfifo()')
+    @unittest.skipIf(sys.platform == "vxworks",
+                    "fifo requires special path on VxWorks")
     def test_copyfile_named_pipe(self):
         try:
             os.mkfifo(TESTFN)