Add missing [privsep_entrypoint]/helper_command

Closes-Bug: ATMOSPHERE-648
Change-Id: I12243527ad763bb249195220093717d68de050f6
diff --git a/roles/nova/vars/main.yml b/roles/nova/vars/main.yml
index f7ba6af..b98b1f0 100644
--- a/roles/nova/vars/main.yml
+++ b/roles/nova/vars/main.yml
@@ -112,6 +112,8 @@
         driver: noop
       os_vif_ovs:
         ovsdb_connection: unix:/run/openvswitch/db.sock
+      privsep_osbrick:
+        helper_command: sudo nova-rootwrap /etc/nova/rootwrap.conf privsep-helper --config-file /etc/nova/nova.conf
       scheduler:
         max_attempts: 3
         workers: 8