Change more tests to use import_module for the modules that
should cause tests to be skipped.  Also rename import_function
to the more descriptive get_attribute and add a docstring.
diff --git a/Lib/test/test_nis.py b/Lib/test/test_nis.py
index 0026953..8d49550 100644
--- a/Lib/test/test_nis.py
+++ b/Lib/test/test_nis.py
@@ -1,6 +1,7 @@
 from test import test_support
 import unittest
-import nis
+
+nis = test_support.import_module('nis')
 
 class NisTests(unittest.TestCase):
     def test_maps(self):