cliff 2.15.0 release

meta:version: 2.15.0
meta:diff-start: -
meta:series: train
meta:release-type: release
meta:pypi: yes
meta:first: yes
meta:release:Author: Tony Breeds <tony@bakeyournoodle.com>
meta:release:Commit: Tony Breeds <tony@bakeyournoodle.com>
meta:release:Change-Id: I75d1a11e330bcd454335b490ccefac430570e957
meta:release:Code-Review+2: Sean McGinnis <sean.mcginnis@gmail.com>
meta:release:Code-Review+1: Dean Troyer <dtroyer@gmail.com>
meta:release:Code-Review+2: Thierry Carrez <thierry@openstack.org>
meta:release:Workflow+1: Thierry Carrez <thierry@openstack.org>
meta:release:Code-Review+1: Jeffrey Williams <jw2610@att.com>