zuul: Add nova-ceph-multistore as a non-voting job

As discussed in I50d3b874b7e0676436c434be6c059f221041560f the tests
introduced by I846b96ef925c34162cf462da91d854ceacabe022 broke
nova-ceph-multistore thanks to the use of
[workarounds]/never_download_image_if_on_rbd in the job and some image
creation in the test that isn't strictly required.

To ensure breakages like this are visable in the future this change adds
the nova-ceph-multistore job as a non-voting job within this repo.

Related-Bug: #1912607
Change-Id: Ifbdaef0b82cc4b1e77e0ecc440e194e5544fe320
1 file changed