horizon 15.1.0 release

meta:version: 15.1.0
meta:diff-start: -
meta:series: stein
meta:release-type: release
meta:pypi: no
meta:first: no
meta:release:Author: Ivan Kolodyazhny <e0ne@e0ne.info>
meta:release:Commit: Akihiro Motoki <amotoki@gmail.com>
meta:release:Change-Id: I50de0cd52f2d43a2d8eb75fb82b06611b6ceb875
meta:release:Code-Review+1: Ivan Kolodyazhny <e0ne@e0ne.info>
meta:release:Code-Review+2: Tony Breeds <tony@bakeyournoodle.com>
meta:release:Code-Review+1: Michelle King <wangyan@awcloud.com>
meta:release:Code-Review+1: Akihiro Motoki <amotoki@gmail.com>
meta:release:Code-Review+1: moser-cui <cuilei@awcloud.com>
meta:release:Code-Review+2: Sean McGinnis <sean.mcginnis@gmail.com>
meta:release:Workflow+1: Sean McGinnis <sean.mcginnis@gmail.com>