network IPAM update in contrail prevents VM from booting in openstack

[Francois Eleouet]

Steps to reproduce:

-Create a VN and associated IPAM
-Change VN IPAM prefix from contrail webUI
-Try to spawn a VM within this network

VM will fail to boot as it attempts to use a deleted subnet uuid (nova compute log):

NeutronClientException: 404-{u'NeutronError': {u'message': u'Subnet 04ab6bdb-0166-456b-8a72-b7a4222d0385 could not be found', u'type': u'ContrailNotFoundError', u'detail': u''}}

It seems to have been introduced by the following commit:

https://github.com/Juniper/contrail-controller/commit/a269b011d91415a60deb19146e6c7f76f4ea5782

[Pedro Marques (5-roque)]

This seems to be a duplicate of #1381779 which is already being worked on.