Adds support for LVM ephemeral storage in Nova

DevStack currently lacks support for LVM ephemeral storage in Nova.
This support is important for testing of Nova's LVM backend. The
proposed change adds a default volume group, to be shared by Cinder
and Nova. It also adds a configuration option NOVA_BACKEND, which
must be LVM if it is set, that determines whether Nova should be
configured to use LVM ephemeral storage.

Change-Id: I4eb9afff3536fbcd563939f2d325efbb845081bb
diff --git a/lib/nova b/lib/nova
index 0e9282b..61216ff 100644
--- a/lib/nova
+++ b/lib/nova
@@ -547,6 +547,11 @@
     iniset $NOVA_CONF DEFAULT ec2_workers "$API_WORKERS"
     iniset $NOVA_CONF DEFAULT metadata_workers "$API_WORKERS"
 
+    if [[ "$NOVA_BACKEND" == "LVM" ]]; then
+        iniset $NOVA_CONF libvirt images_type "lvm"
+        iniset $NOVA_CONF libvirt images_volume_group $DEFAULT_VOLUME_GROUP_NAME
+    fi
+
     if is_ssl_enabled_service glance || is_service_enabled tls-proxy; then
         iniset $NOVA_CONF DEFAULT glance_protocol https
     fi