Description of problem:
The Neutron L3HA feature does work on a standard deployment, however it only works for the first router created on a given external network. When trying to add two or three routers to the same external network in the same tenant, the ports do not come up. 

Version-Release number of selected component (if applicable):


How reproducible:
100%

Steps to Reproduce:
1.Deploy HA overcloud
2.Create external network
3. Create two routers both attached to same external network

Actual results:
Second routers HA ports fail to come up

Expected results:
I can attach many routers to an external network in the same tenant

Additional info:
I have been using this feature since liberty and it usually just works. My setup is pretty basic. 

I am using isolated networks
I used tripleo to deploy

neutron-openvswitch-agent throws this error on the second routers creation

2017-12-21 07:25:34.848 961672 WARNING neutron.agent.rpc [req-ec84870c-0a83-4495-8883-737c639c9603 - - - - -] Device Port(admin_state_up=True,allowed_address_pairs=[],binding=PortBinding,binding_levels=[],created_at=2017-12-21T12:25:27Z,data_plane_status=<?>,description='',device_id='694913ed-6464-43fa-8372-7722b81c4d7a',device_owner='network:router_ha_interface',dhcp_options=[],distributed_binding=None,dns=None,fixed_ips=[IPAllocation],id=45992ab1-d323-4697-afb1-babc1473b3ac,mac_address=fa:16:3e:70:da:02,name='HA port tenant baa55f0b597242868c715e4e18e5fab4',network_id=88e10101-4675-48fa-aa65-e945b3146915,project_id='',qos_policy_id=None,revision_number=5,security=PortSecurity(45992ab1-d323-4697-afb1-babc1473b3ac),security_group_ids=set([]),status='DOWN',updated_at=2017-12-21T12:25:34Z) is not bound.
2017-12-21 07:25:34.855 961672 WARNING neutron.plugins.ml2.drivers.openvswitch.agent.ovs_neutron_agent [req-ec84870c-0a83-4495-8883-737c639c9603 - - - - -] Device 45992ab1-d323-4697-afb1-babc1473b3ac not defined on plugin or binding failed