Comment 9 for bug 1427772

Since change https://review.openstack.org/#/c/496031/ we're still allocating resources against the forced destination host during live migration using placement, which for the FilterScheduler at least should be accurate and good since it will tell us if there isn't enough free memory on the host to fix the instance.

I think that means _check_destination_has_enough_memory is only needed then for people using the CachingScheduler because the CachingScheduler isn't using Placement so capacity information on the host wouldn't be accurate (the inventory for the resource provider is getting reported by the allocations for all of the other instances on that host might not be reported since the CachingScheduler doesn't allocate them during scheduling). So the RAMFilter type check in _check_destination_has_enough_memory is still needed for the CachingScheduler, which is deprecated.

We should be able to remove the CachingScheduler and _check_destination_has_enough_memory check in Stein now that we have the "nova-manage placement heal_allocations" CLI which CachingScheduler deployments can use to create allocations in placement for their existing instances.