Python 3: enable tests/unit/middleware/test_request_id.py

In Python 3, webob will return bytes, so we need to fix generate_request_id()
so that it also returns bytes. The behaviour is unchanged in Python 2.

Change-Id: I389cf20e4c999c9bb576a42388497852f8ba27ec
Fix test_gettextutils on Python 3

On Python 3, str(obj) calls obj.__str__(), not obj.__unicode__().

The test does not pass with nosetests, LogLevelTranslationsTest fails with an
AttributeError (self.level is missing), because nosetests doesn't play well
with test scenarios.

Change-Id: I78ae106e336480d9995ac4394197ea45b8ef9b07
Merge "Python 3: enable tests/unit/middleware/test_request_id.py"
Merge "Fix test_gettextutils on Python 3"