Comment 9 for bug 1442121

I had a look at the other Neutron resources now and there is only one other potential trouble spot where the same kind of thing (looking up a resource ID from Neutron without exception handling) happens:

https://github.com/openstack/heat/commit/547457828ded4c4d8ecec1546703cd154b8e4a8c#diff-f62d2ab8ef023c0a756f83e1209d1e9cR62

At first glance it does not appear to be related to that commit's message, but I might be wrong. Is that lookup really neccessary? As far as I understand (correct me if I'm wrong) it yields the same Router ID that is already recorded in the RouterInterface's properties. If it is required I'll add exception handling in that spot as well: after all a RouterInterface with no associated Router is functionally equivalent to a RouterInterface with no associated Subnet. It does not need to be part of the dependency graph since it is just a piece of stale information in Heat's database.