Traceback from comment 11 is not the cause for network delete failure, it rather shows that db retry works. Logs from snapshot show that port failed to be deleted first time (DBDeadlock), but then was  deleted on a second attempt (thanks to db retry). 

Network deletion failure was caused by ObjectDeletedError. So this is not a regression, I'd suggest to open another bug for this.

There is a race on network deletion where dhcp ports of the network may be deleted concurrently: by dhcp agent issuing port deletion on server side and by neutron server itself  when deleting network. This may lead to ObjectDeletedError on one of neutron servers. Traceback:

2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin Traceback (most recent call last):
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/neutron/plugins/ml2/plugin.py", line 681, in _delete_ports
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     self.delete_port(context, port.id)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/oslo_db/api.py", line 131, in wrapper
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     return f(*args, **kwargs)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/neutron/plugins/ml2/plugin.py", line 1288, in delete_port
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     super(Ml2Plugin, self).delete_port(context, id)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/neutron/db/db_base_plugin_v2.py", line 1915, in delete_port
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     self._delete_port(context, id)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/neutron/db/db_base_plugin_v2.py", line 1938, in _delete_port
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     query.delete()
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/query.py", line 2670, in delete
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     delete_op.exec_()
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 896, in exec_
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     self._do_pre_synchronize()
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 958, in _do_pre_synchronize
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     eval_condition(obj)]
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/evaluator.py", line 115, in evaluate
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     left_val = eval_left(obj)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/evaluator.py", line 72, in <lambda>
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     return lambda obj: get_corresponding_attr(obj)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/attributes.py", line 239, in __get__
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     return self.impl.get(instance_state(instance), dict_)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/attributes.py", line 589, in get
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     value = callable_(state, passive)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/state.py", line 424, in __call__
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     self.manager.deferred_scalar_loader(self, toload)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin   File "/usr/lib/python2.7/dist-packages/sqlalchemy/orm/loading.py", line 614, in load_scalar_attributes
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin     raise orm_exc.ObjectDeletedError(state)
2015-07-30 14:07:59.476 20498 TRACE neutron.plugins.ml2.plugin ObjectDeletedError: Instance '<Port at 0x7f4ed51ceb10>' has been deleted, or its row is otherwise not present.