Comment 17 for bug 1752152

I audited the stable/pike code. While https://review.openstack.org/#/c/469579/ went into pike, and is used if we actually create/update/delete volume attachments, we don't actually call any of those flows. We didn't start creating new style attachments until Queens. Some of the plumbing was added in Pike, but not actually 'turned on' in the API at that point, so we shouldn't need to backport any fixes to stable/pike.