This change adds new THT parameters `NovaLibvirtCPUMode`,
`NovaLibvirtCPUModels` and `NovaLibvirtCPUModelExtraFlags`
which allows to configure `libvirt/cpu_mode`, `libvirt/cpu_model`
and `libvirt/cpu_model_extra_flags` parameters respectively.
NOTE: This backport is slightly different from master patch
because of following reasons:
- Change [1] deprecates `libvirt/cpu_model` in favor
of `libvirt/cpu_models` parameter.
- Change [2] removes redundant `libvirt_` prefix from
parameter names.
[1] Ib8e9ec2e0bde59e72b0ce3639b64d3e8a6ff9eac
[2] I44dc4e44411657f0c0d6f35051675b12ce77fdef
Change-Id: I8df21d5d171976cbb8670dc5aef744b5fae657b2
(cherry picked from commit 772b7398a7)
f9df16fc85