Convert unicode strings for python3 portability

From http://docs.python.org/3.1/whatsnew/3.0.html

You can no longer use u"..." literals for Unicode text.
However, you must use b"..." literals for binary data. Use
python-six to make this migration easier.

Change-Id: I95166a07f4edf33be55a4bdf2674c2f238a06f19
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Stylistic improvements from quantum-rootwrap

As part of the convergence effort between oslo-rootwrap and
quantum-rootwrap, import stylistic improvements introduced
in quantum-rootwrap, like:

- HACKING-compliant docstrings
- More elegant return construct from match_filter in filters.py
- Remove overridden use of filters in wrapper.py

Change-Id: I49a97271b1c385feb25adf4f62add5c71962b5dd
Merge "Stylistic improvements from quantum-rootwrap"
Merge "Convert unicode strings for python3 portability"