Comment 3 for bug 1637449

The logic here [0] indeed seems to be incorrect, eg in case of there is
a node in available state with instance_uuid set, first the driver will
report vcpus=vcpus_used=properties['vcpus'] and then will set vcpus=0
leaving vcpus_used intact.

My proposal here is the following:

* If there is an instance_uuid on the node, no matter what provision/power
  state it's in, consider the resources as used. In case it's an orphan,
  an admin will need to take some manual action anyway.

* If there is no instance_uuid and a node is in cleaning/clean wait after
  tear down, it is a part of normal node lifecycle, report all resources
  as used. This means we need a way to determine if it's a manual or
  automated clean.

* If there is no instance_uuid, and a node:
  - has a bad power state or
  - is in maintenance
  - manual clean is happening
  or actually in any other case, consider it unavailable, report available
  resources = used resources = 0. Provision state does not matter in this
  logic, all cases that we wanted to take into account are described in
  the first two bullets.

[0] https://github.com/openstack/nova/blob/1506c36b4446f6ba1487a2d68e4b23cb3fca44cb/nova/virt/ironic/driver.py#L262