tests/base_test.py: Use __name__ for Flask's import_name

Avoid several test failures like:

    ======================================================================
    ERROR: test_credentialed_request (tests.test_credentials.AppConfigExposeHeadersTestCase)
    AppConfigExposeHeadersTestCase.test_credentialed_request
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/.../tests/base_test.py", line 82, in setUp
        self.app = Flask(self.__class__.__name__)
      File "/usr/lib64/python3.4/site-packages/flask/app.py", line 319, in __init__
        template_folder=template_folder)
      File "/usr/lib64/python3.4/site-packages/flask/helpers.py", line 741, in __init__
        self.root_path = get_root_path(self.import_name)
      File "/usr/lib64/python3.4/site-packages/flask/helpers.py", line 631, in get_root_path
        loader = pkgutil.get_loader(import_name)
      File "/usr/lib64/python3.4/pkgutil.py", line 469, in get_loader
        return find_loader(fullname)
      File "/usr/lib64/python3.4/pkgutil.py", line 490, in find_loader
        return spec.loader
    AttributeError: 'NoneType' object has no attribute 'loader'

on Python 3.4 [1].  The solution is to use an importable name [2]:

> About the First Parameter
>
> The idea of the first parameter is to give Flask an idea what
> belongs to your application. This name is used to find resources on
> the file system, can be used by extensions to improve debugging
> information and a lot more.
>
> So it’s important what you provide there. If you are using a single
> module, __name__ is always the correct value. If you however are
> using a package, it’s usually recommended to hardcode the name of
> your package there.

Previously we were using the class name (not the module name), but you
can't use that to import anything ;).

[1]: https://github.com/mitsuhiko/flask/issues/1011
[2]: http://flask.pocoo.org/docs/0.10/api/#flask.Flask