set cpu_model to Nehalem for kvm jobs

RHEL 9 and Ubuntu Jammy are being compiled for the x86_64-v2
architecture which is newer than the qemu default of qemu64.
Nehalem is apparently the oldest model that works for x86_64-v2
and is expected to work on Intel and AMD cpus with kvm or qemu.

See devstack change [0].

[0]: Ibd6e11b59f3c8655bc60ace7383a08458b2177f2

Depends-on: https://review.opendev.org/c/openstack/kayobe/+/872981

Change-Id: I09567b4cce95ff1fe2fe4e9e91e49d5f5082f7d0

Author: bbezak

etc/kayobe/kolla/config/nova/nova-compute.conf

@@ -0,0 +1,11 @@
+{% raw %}
+[libvirt]
+# RHEL 9 and Ubuntu Jammy are being compiled for the x86_64-v2
+# architecture which is newer than the qemu default of qemu64.
+# Nehalem is apparently the oldest model that works for x86_64-v2
+# and is expected to work on Intel and AMD cpus with kvm or qemu.
+{% if nova_compute_virt_type == 'kvm' %}
+cpu_mode=custom
+cpu_model=Nehalem
+{% endif %}
+{% endraw %}