Comment 1 for bug 1724589

From IRC, my way of describing the problem:

(9:24:05 AM) mriedem: do you mean the custom resource class allocatoin isn't showing up for the instance?
(9:24:37 AM) johnthetubaguy: I mean old instances don't have allocations for the new resource, which breaks the scheduling of new flavors that use the resource class
(9:24:50 AM) mriedem: so instance A had vcpu/ram/disk allocations before the node.resource_class was set, then you set node.resource_class = baremetal and now you expect to see a 'baremetal' allocation for instance A in placement
(9:25:17 AM) johnthetubaguy: that is what I expected, yes
(9:25:24 AM) johnthetubaguy: (clearly incorrectly)
(9:25:31 AM) mriedem: that's probably because the RT isn't reporting allocations anymore once all of your computes are pike

(9:27:48 AM) mriedem: johnthetubaguy: ok so the scheduling issue is a new instance request can try to claim the 'baremetal' resource on node A even though instance A is already using it
(9:27:52 AM) mriedem: which causes a scheduler failure yes?
(9:28:00 AM) johnthetubaguy: mriedem: yes

We made a similar sounding fix in Pike https://review.openstack.org/#/c/492964/ but that was for reporting inventory with the new node.resource_class, not for updating instance allocations for a migrated flavor/instance.