In same cases, the hypervisor presents to the guest OS a named CPU model
is similar to the host CPU and adds extra features to approximate the
host model. However, this does not guarantee all features will be
precisely match.
This patch adds LIBVIRT_CPU_MODE to allow users to define the CPU mode
they want to use, for example "host-passthrough".
Change-Id: I83792c776b50d1d22584be2a37cc6a166f09c72b
8dd6f153d6