build fails with 'operating-system: already provided'

Failure in dummy CI run:

2018-03-23 18:56:34.270457 | primary | 2018-03-23 18:56:34.267 | diskimage_builder.element_dependencies.AlreadyProvidedException: operating-system: already provided by ['manila-ubuntu-minimal']
2018-03-23 18:56:34.275333 | primary | ERROR: InvocationError: '/home/zuul/workspace/.tox/buildimage/bin/manila-image-create'
2018-03-23 18:56:34.275793 | primary | ___________________________________ summary ____________________________________
2018-03-23 18:56:34.275897 | primary | ERROR: buildimage: commands failed
2018-03-23 18:56:34.514369 | primary | ERROR
2018-03-23 18:56:34.514789 | primary | {
2018-03-23 18:56:34.514933 | primary | "delta": "0:00:29.481569",
2018-03-23 18:56:34.515071 | primary | "end": "2018-03-23 18:56:34.291594",
2018-03-23 18:56:34.515200 | primary | "failed": true,
2018-03-23 18:56:34.515332 | primary | "rc": 1,
2018-03-23 18:56:34.515498 | primary | "start": "2018-03-23 18:56:04.810025"
2018-03-23 18:56:34.515654 | primary | }

Log: http://logs.openstack.org/94/555894/1/check/legacy-manila-buildimage-generic/b8b29e4/job-output.txt.gz#_2018-03-23_18_56_34_270457