pbr 3.1.1 release

meta:version: 3.1.1
meta:diff-start: -
meta:series: independent
meta:release-type: release
meta:pypi: yes
meta:first: no
meta:release:Author: Julien Danjou <julien@danjou.info>
meta:release:Commit: Julien Danjou <julien@danjou.info>
meta:release:Change-Id: I2277e20302cd8bbdbe46fc09c143a2def328bd1f
meta:release:Code-Review+1: Tony Breeds <tony@bakeyournoodle.com>
meta:release:Code-Review+1: ChangBo Guo(gcb) <glongwave@gmail.com>
meta:release:Code-Review+2: Thierry Carrez <thierry@openstack.org>
meta:release:Workflow+1: Thierry Carrez <thierry@openstack.org>