havana: nova Add cpuset attr to vcpu conf in libvirt xml

[Tom Fifield]

https://review.openstack.org/#/c/26363/ adds a new feature to nova

Add cpuset attr to vcpu conf in libvirt xml

Currently the instances can use all of the pcpu of compute node, the
host may become slow when vcpus of instances are busy, so we need to
pin vcpus to the specific pcpus of host instead of all pcpus.
Also added a cache of total vcpus num in libvirt driver here.

[Tom Fifield (fifieldt)]

The nova.conf option is called 'vcpu_pin_set', with default=None,

helptext: Which pcpus can be used by vcpus of instance 'e.g: "4-12,^8,15"'),

The blueprint is: https://blueprints.launchpad.net/nova/+spec/auto-cpu-pinning

and describes that this is automatic pinning - not user controlled.

[Anne Gentle (annegentle)]

Confirmed that this vcpu_pin_set setting is in the config ref, since this is not user-facing, marking fix released.