libvirt: excessive warning logs like "couldn't obtain the vcpu count from domain id: 6bcf0dcb-722f-44a3-a0aa-3fa42dd1075a, exception: Requested operation is not valid: cpu affinity is not supported"

These warnings show up a ton which means they probably shouldn't be warnings:

http://logs.openstack.org/79/368079/2/check/gate-tempest-dsvm-neutron-multinode-full-ubuntu-xenial/9a1a7f0/logs/screen-n-cpu.txt.gz?level=TRACE

2016-09-10 21:29:16.759 20105 WARNING nova.virt.libvirt.driver [req-386e6a64-0d9c-48ec-bab9-4acabdf55265 - -] couldn't obtain the vcpu count from domain id: 6bcf0dcb-722f-44a3-a0aa-3fa42dd1075a, exception: Requested operation is not valid: cpu affinity is not supported

http://logstash.openstack.org/#dashboard/file/logstash.json?query=message%3A%5C%22couldn't%20obtain%20the%20vcpu%20count%20from%20domain%20id%5C%22%20AND%20message%3A%5C%22exception%3A%20Requested%20operation%20is%20not%20valid%3A%20cpu%20affinity%20is%20not%20supported%5C%22%20AND%20tags%3A%5C%22screen-n-cpu.txt%5C%22&from=7d

220K+ times in 7 days in the gate so this is excessive.

The warning is here:

https://github.com/openstack/nova/blob/e92d7537d67c7eb0e49415b429d56be762e02679/nova/virt/libvirt/driver.py#L4922

If cpu affinity is not supported, we shouldn't log that as a warning.

I'm not sure if this is something with the guest configuration or with the version of libvirt/qemu on the host, we might need to ask danpb in the #openstack-nova irc channel.