_restore_local_vlan_map raises exception for untagged flat networks

[Eric Larese]

This line:

https://github.com/openstack/neutron/blob/master/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py#L359

can raise exception when _restore_local_vlan_map runs in environments with flat or untagged VLAN networks. For example:

  File "/usr/lib/python2.7/site-packages/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py", line 301, in __init__
     self._restore_local_vlan_map()
   File "/usr/lib/python2.7/site-packages/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py", line 360, in _restore_local_vlan_map
     'segmentation_id']),
 ValueError: invalid literal for int() with base 10: 'None'

It appears the reason for this is because the command "ovs-vsctl list Port" is returning port entries that have segmentation_id as None, for example like this:

other_config : {net_uuid="34baaa59-db42-4551-a1f0-0b2af85c288b", network_type=flat, physical_network=default, segmentation_id=None}

This code already handles the case where net_uuid is missing or local_vlan is DEAD_VLAN_TAG, but I think it should also handle the case where segmentation_id is missing.