CORD-2964 add TOSCA example for creating VM

Change-Id: I41711f32f84dbeaf659b535a853993295d1a136f
diff --git a/xos/synchronizer/steps/sync_openstackserviceinstance.py b/xos/synchronizer/steps/sync_openstackserviceinstance.py
index 6ae91a1..9db35de 100644
--- a/xos/synchronizer/steps/sync_openstackserviceinstance.py
+++ b/xos/synchronizer/steps/sync_openstackserviceinstance.py
@@ -88,6 +88,9 @@
 
             # TODO(smbaker): No ssh keys specified
 
+            if not instance.node:
+                raise Exception("No node specified for instance")
+
             availability_zone="nova:%s" % instance.node.name
 
             log.info("Creating Instance", instance=instance, image_id=image_id, flavor_id=flavor_id,