dotest.py: bugfix: test filters with -f do not work on Python3

[lawrence_danna]

Summary

dotest -f does not work on Python3.

The name types.UnboundMethodType was an alias for types.MethodType in
2.7, but it does not exist in python3. MethodType works in both.

Also the actual type returned from SomeClass.some_method in python3
will be types.Function, not MethodType.

[JDevlieghere]

I would prefer to update the unittest2 dependency instead, but I tried doing so and it appears to be less straightforward than I'd hoped. I have added it to my todo-list, but this is fine in the meantime.

lldb/third_party/Python/module/unittest2/unittest2/loader.py

def loadTestsFromName(self, name, module=None):
         obj = module
         for part in parts:
             parent, obj = obj, getattr(obj, part)
 
         if isinstance(obj, types.ModuleType):
             return self.loadTestsFromModule(obj)
         elif isinstance(obj, type) and issubclass(obj, unittest.TestCase):
             return self.loadTestsFromTestCase(obj)
-        elif (isinstance(obj, types.UnboundMethodType) and
+        elif (isinstance(obj, (types.MethodType, types.FunctionType)) and
               isinstance(parent, type) and
               issubclass(parent, case.TestCase)):
             return self.suiteClass([parent(obj.__name__)])
         elif isinstance(obj, unittest.TestSuite):
             return obj
         elif hasattr(obj, '__call__'):
             test = obj()
             if isinstance(test, unittest.TestSuite):