testenv: use host-model/host-passthru as a CPU model for VMs

By default, QEMU uses "qemu64" model that does not support x86-64-v2
features required for CentOS/RHEL 9. Use the appropriate host model
option depending on whether KVM or emulation is used.

Change-Id: Idf191547044b12c7acdbd6d3962c541a1b8c6d03

playbooks/roles/bifrost-create-vm-nodes/templates/testvm.xml.j2

@@ -13,6 +13,11 @@
     <bootmenu enable='no'/>
     <bios useserial='yes' rebootTimeout='10000'/>
   </os>
+  {% if test_vm_domain_type == 'kvm' %}
+  <cpu mode='host-passthrough'/>
+  {% else %}
+  <cpu mode='host-model'/>
+  {% endif %}
   <features>
     <acpi/>
     <apic/>