Using upgrade.old_release in nova.upgrade.pre state

The patch makes the formula use upgrade.old_release while rendering
nova.conf in nova.upgrade.pre state because of the fact that at that
point old release of OpenStack is still installed.

Change-Id: Ifbaa7f37d33091cdb984b0e3d65f323bb457b2df
Related-PROD: PROD-27270 (PROD:27270)
diff --git a/nova/upgrade/pre/init.sls b/nova/upgrade/pre/init.sls
index 9ed049a..0c5834e 100644
--- a/nova/upgrade/pre/init.sls
+++ b/nova/upgrade/pre/init.sls
@@ -16,7 +16,7 @@
 /etc/nova/nova.conf:
   file.managed:
   - name: /etc/nova/nova.conf
-  - source: salt://nova/files/{{ _data.version }}/nova-{{ type }}.conf.{{ grains.os_family }}
+  - source: salt://nova/files/{{ upgrade.old_release }}/nova-{{ type }}.conf.{{ grains.os_family }}
   - template: jinja
 
 {%- if controller.get('enabled') %}