Description of problem: https://bugs.launchpad.net/cinder/+bug/1472710 Sometimes we can get into a state where a Purity host is deleted before we try and disconnect a volume from it. There is a fix in Cinder that has been backported to stable/kilo, https://review.openstack.org/#/c/228219/ which will need to be included in OSP 7
This patch is merged in to the stable kilo upstream https://review.openstack.org/#/c/228219/ so we'll get the fix in the next async for free.