[devscripts] Preserve host-passthrough CPU in metal3 devscripts

[danpawlik]

The metal3 generates a file in work dir:

# metal3-dev-env/vm-setup/roles/libvirt/tasks/vm_setup_tasks.yml
(...)
- name: Detect virtualization if libvirt_domain_type is not provided
  command: systemd-detect-virt
  ignore_errors: true
  become: true
  register: virt_result

- name: Default to qemu if inside a VM
  set_fact:
    libvirt_domain_type: qemu
  when: virt_result is succeeded

- name: Default to kvm if a VM is not detected
  set_fact:
    libvirt_domain_type: kvm
  when: virt_result is failed
when: libvirt_domain_type is undefined

which generates later in an SNO VM xml:

<cpu mode='custom' match='exact' check='full'>
  <model fallback='forbid'>EPYC</model>
  <vendor>AMD</vendor>
  <feature policy='require' name='monitor'/>
  <feature policy='require' name='x2apic'/>
  <feature policy='require' name='hypervisor'/>
  <feature policy='require' name='acpi'/>
  <feature policy='require' name='ss'/>
  <feature policy='require' name='erms'/>
  <feature policy='require' name='mpx'/>
  <feature policy='require' name='clwb'/>
  <feature policy='require' name='umip'/>
  <feature policy='require' name='pku'/>
  <feature policy='require' name='vaes'/>
  <feature policy='require' name='la57'/>
  <feature policy='require' name='rdpid'/>
  <feature policy='require' name='pks'/>
  <feature policy='require' name='fsrm'/>
  <feature policy='require' name='cmpccxadd'/>
  <feature policy='require' name='fzrm'/>
  <feature policy='require' name='fsrs'/>
  <feature policy='require' name='fsrc'/>
  <feature policy='require' name='3dnowext'/>
  <feature policy='require' name='3dnow'/>
  <feature policy='require' name='xsaveerptr'/>
  <feature policy='require' name='wbnoinvd'/>
  <feature policy='require' name='npt'/>
  <feature policy='require' name='vgif'/>
  <feature policy='require' name='svme-addr-chk'/>
  <feature policy='require' name='no-nested-data-bp'/>
  <feature policy='require' name='null-sel-clr-base'/>
  <feature policy='disable' name='vme'/>
  <feature policy='disable' name='xsavec'/>
  <feature policy='disable' name='misalignsse'/>
  <feature policy='disable' name='osvw'/>
  <feature policy='disable' name='topoext'/>
  <feature policy='disable' name='fxsr_opt'/>
  <feature policy='disable' name='nrip-save'/>
</cpu>

instead of host-passthrough. Bypass that behavior and always use
host-passthrough.

[openshift-ci]

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[abays]

/lgtm