More python3 compatibility.

* pbr/packaging.py: Properly convert bytes into unicode strings and back
to bytes again. Replace os.path.walk() with os.walk().

* pbr/tests/__init__.py: Remove use of mox.

* pbr/tests/moxstubout.py: Remove use of mox.

* pbr/tests/test_setup.py: Use bytestrings instead of str or unicode
when performing IO.

* pbr/tests/test_version.py: Remove use of oslo.config.

* requirements.txt: Pin jinja2 to version compatible with python3.2.

* test-requirements.txt: Remove oslo.config and mox.

Change-Id: I9b5a32d7204fa2af56ecf4fdcf6b6da3bbb03200
Merge "More python3 compatibility."