Fix test_ctypes failure on OpenIndiana buildbot where _ctypes is not built

Lib/test/test_ctypes.py

 import unittest
+from test.support import import_module
 
-from ctypes.test import load_tests
+ctypes_test = import_module('ctypes.test')
+
+load_tests = ctypes_test.load_tests
 
 if __name__ == "__main__":
     unittest.main()