Unittest - Bring back diag() for generating TAP output

* Still needs work to make sure output is displayed after the test
status (not ok ...) and not before.

test/tw-285.t

@@ -32,10 +32,10 @@ import unittest
 # Ensure python finds the local simpletap and basetest modules
 sys.path.append(os.path.dirname(os.path.abspath(__file__)))
 
-from basetest import Task
+from basetest import Task, TestCase
 
 
-class Test285(unittest.TestCase):
+class Test285(TestCase):
     @classmethod
     def setUpClass(cls):
         cls.t = Task()