Add ability to set cpu_model on compute

This patch adds ability to set cpu_model from libvirt section
on compute node.

Change-Id: Iaac78ec9e39fb1f6806e61344316b53576508516
Related-Prod: PROD-19272
diff --git a/nova/files/pike/nova-compute.conf.Debian b/nova/files/pike/nova-compute.conf.Debian
index d7854af..f41d26b 100644
--- a/nova/files/pike/nova-compute.conf.Debian
+++ b/nova/files/pike/nova-compute.conf.Debian
@@ -6456,7 +6456,12 @@
 #   This would result in an error and the instance won't be launched.
 # * ``virt_type``: Only the virtualization types ``kvm`` and ``qemu`` use this.
 #  (string value)
+{%- if compute.get('libvirt', {}).get('cpu_model') is defined %}
+cpu_model = {{ compute.libvirt.cpu_model }}
+{%- else %}
 #cpu_model=<None>
+{%- endif %}
+
 
 # Location where libvirt driver will store snapshots before uploading them to
 # image service (string value)