Fixing logic for cpu_model parameter
Backporting from pike to ocata and newton
Adding docs and tests

Prod-Related: PROD-19272

Change-Id: I8948f48e4ef57ece3ccdee76a5152536cced5a3c
diff --git a/tests/pillar/compute_single.sls b/tests/pillar/compute_single.sls
index abaa7ad..08250ba 100644
--- a/tests/pillar/compute_single.sls
+++ b/tests/pillar/compute_single.sls
@@ -1,12 +1,15 @@
 nova:
   compute:
-    version: liberty
+    version: newton
     enabled: true
     virtualization: kvm
     heal_instance_info_cache_interval: 60
     vncproxy_url: openstack:6080
     vnc_keymap: en-gb
     resume_guests_state_on_host_boot: False
+    cpu_mode: custom
+    libvirt:
+      cpu_model: IvyBridge
     bind:
       vnc_address: 127.0.0.1
       vnc_port: 6080