py-pbr: updated to 5.4.4

5.4.4
* trivial: Use 'open' context manager
* Update to latest hacking
* Mark strings as raw

5.4.2
* Add Python 3 Train unit tests

5.4.1
* Fix parsing on egg names with dashes from git URLs

5.4.0
* option to print only the version of a package

5.3.1
* Resolve some issue with tox.ini, setup.cfg

5.3.0
* Stop using pbr sphinx integration
* Switch to release.o.o for constraints
* Make WSGI tests listen on localhost
* Fix Windows support
* Allow git-tags to be SemVer compliant
* Read description file as utf-8

(adam)