Not Authorized response from neutron causes nova to traceback with AttributeError

version: stable/icehouse from 2014.2.2 onwards (does not impact stable/{juno|kilo})

nova-api fails to handle Not Authorized from neutron:

2015-04-20 00:49:29.399 22741 TRACE nova.api.openstack action_result = self.dispatch(meth, request, action_args)
2015-04-20 00:49:29.399 22741 TRACE nova.api.openstack File "/usr/lib/python2.6/site-packages/nova/api/openstack/wsgi.py", line 1078, in dispatch
2015-04-20 00:49:29.399 22741 TRACE nova.api.openstack return method(req=request, **action_args)
2015-04-20 00:49:29.399 22741 TRACE nova.api.openstack File "/usr/lib/python2.6/site-packages/nova/api/openstack/compute/contrib/floating_ips.py", line 187, in delete
2015-04-20 00:49:29.399 22741 TRACE nova.api.openstack except exception.Forbidden:
2015-04-20 00:49:29.399 22741 TRACE nova.api.openstack AttributeError: 'module' object has no attribute 'Forbidden'

due to a bad backport landed in upstream stable/icehouse:

  https://github.com/openstack/nova/commit/4bc680f2

which uses a juno-era exception class.

Turns out this broken patch has been in the last two upstream stable/icehouse releases (2014.2.3, 2104.2.4).