Update to pbr and flake8.

As part of this, found a discrepancy between the git tags and what was in
libra.__version__ - which is the whole reason to do tag-based-versions anyway.
After landing this, someone should do a "tag -s 1.2" or something similar
to release a properly tagged version of the code.

Change-Id: I2bb678bc6928dffebb0abc7c67cec50642b1f43d