Add LIBVIRT_CPU_MODE to set CPU mode

In same cases, the hypervisor presents to the guest OS a named CPU model
is similar to the host CPU and adds extra features to approximate the
host model. However, this does not guarantee all features will be
precisely match.

This patch adds LIBVIRT_CPU_MODE to allow users to define the CPU mode
they want to use, for example "host-passthrough".

Change-Id: I83792c776b50d1d22584be2a37cc6a166f09c72b

Author: cgoncalves

lib/nova

@@ -259,6 +259,7 @@ function configure_nova {
                 if [ ! -e /dev/kvm ]; then
                     echo "WARNING: Switching to QEMU"
                     LIBVIRT_TYPE=qemu
+                    LIBVIRT_CPU_MODE=none
                     if which selinuxenabled >/dev/null 2>&1 && selinuxenabled; then
                         # https://bugzilla.redhat.com/show_bug.cgi?id=753589
                         sudo setsebool virt_use_execmem on

lib/nova_plugins/hypervisor-libvirt

@@ -39,7 +39,7 @@ function cleanup_nova_hypervisor {
 function configure_nova_hypervisor {
     configure_libvirt
     iniset $NOVA_CONF libvirt virt_type "$LIBVIRT_TYPE"
-    iniset $NOVA_CONF libvirt cpu_mode "none"
+    iniset $NOVA_CONF libvirt cpu_mode "$LIBVIRT_CPU_MODE"
     # Do not enable USB tablet input devices to avoid QEMU CPU overhead.
     iniset $NOVA_CONF DEFAULT pointer_model "ps2mouse"
     iniset $NOVA_CONF libvirt live_migration_uri "qemu+ssh://$STACK_USER@%s/system"

stackrc

@@ -625,6 +625,7 @@ VIRT_DRIVER=${VIRT_DRIVER:-$DEFAULT_VIRT_DRIVER}
 case "$VIRT_DRIVER" in
     ironic|libvirt)
         LIBVIRT_TYPE=${LIBVIRT_TYPE:-kvm}
+        LIBVIRT_CPU_MODE=${LIBVIRT_CPU_MODE:-none}
         if [[ "$os_VENDOR" =~ (Debian|Ubuntu) ]]; then
             # The groups change with newer libvirt. Older Ubuntu used
             # 'libvirtd', but now uses libvirt like Debian. Do a quick check