unittest: TestCase: Add (dummy) __init__.

Mostly to workaround inherited MicroPython's issues with inheritance.

Signed-off-by: Paul Sokolovsky <pfalcon@users.sourceforge.net>

python-stdlib/unittest/unittest.py

@@ -30,6 +30,9 @@ class AssertRaisesContext:
 
 
 class TestCase:
+    def __init__(self):
+        pass
+
     def fail(self, msg=""):
         assert False, msg