Something

I commented out the whole section and ran 

/opt/openstack-ansible/playbooks$ sudo openstack-ansible os-neutron-install.yml 

 #  - network:
  #      container_bridge: "br-vlan"
  #      container_type: "veth"
  #      container_interface: "eth12"
  #      host_bind_override: "eth12"
  #      type: "flat"
  #      net_name: "flat"
  #      group_binds:
  #        - neutron_linuxbridge_agent


now my log looks better:
2018-02-07 16:13:20.014 16479 INFO neutron.common.config [-] /openstack/venvs/neutron-16.0.6/bin/neutron-linuxbridge-agent version 11.0.3.dev24
2018-02-07 16:13:20.015 16479 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Interface mappings: {'flat': 'eth12', 'vlan': 'br-vlan'}
2018-02-07 16:13:20.015 16479 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Bridge mappings: {}
2018-02-07 16:13:20.023 16479 ERROR neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Interface eth12 for physical network flat does not exist. Agent terminated!
2018-02-07 16:13:24.785 16594 INFO neutron.common.config [-] Logging enabled!
2018-02-07 16:13:24.785 16594 INFO neutron.common.config [-] /openstack/venvs/neutron-16.0.6/bin/neutron-linuxbridge-agent version 11.0.3.dev24
2018-02-07 16:13:24.786 16594 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Interface mappings: {'vlan': 'br-vlan'}
2018-02-07 16:13:24.786 16594 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Bridge mappings: {}
2018-02-07 16:13:24.808 16594 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Agent initialized successfully, now running...
2018-02-07 16:13:25.222 16594 INFO neutron.plugins.ml2.drivers.agent._common_agent [req-03caceda-d83e-438a-874a-6ca8eba5520d - - - - -] RPC agent_id: lb58ac785a22fe
2018-02-07 16:13:25.234 16594 INFO neutron.agent.agent_extensions_manager [req-03caceda-d83e-438a-874a-6ca8eba5520d - - - - -] Loaded agent extensions: []
2018-02-07 16:13:25.519 16594 INFO neutron.plugins.ml2.drivers.agent._common_agent [req-03caceda-d83e-438a-874a-6ca8eba5520d - - - - -] Linux bridge agent Agent RPC Daemon Started!
2018-02-07 16:13:25.520 16594 INFO neutron.plugins.ml2.drivers.agent._common_agent [req-03caceda-d83e-438a-874a-6ca8eba5520d - - - - -] Linux bridge agent Agent out of sync with plugin!
2018-02-07 16:13:25.684 16594 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.arp_protect [req-03caceda-d83e-438a-874a-6ca8eba5520d - - - - -] Clearing orphaned ARP spoofing entries for devices []
2018-02-07 16:13:32.438 16594 INFO neutron.plugins.ml2.drivers.agent._common_agent [-] Stopping Linux bridge agent agent.
2018-02-07 16:13:36.861 16827 INFO neutron.common.config [-] Logging enabled!
2018-02-07 16:13:36.862 16827 INFO neutron.common.config [-] /openstack/venvs/neutron-16.0.6/bin/neutron-linuxbridge-agent version 11.0.3.dev24
2018-02-07 16:13:36.862 16827 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Interface mappings: {'vlan': 'br-vlan'}
2018-02-07 16:13:36.862 16827 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Bridge mappings: {}
2018-02-07 16:13:36.887 16827 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.linuxbridge_neutron_agent [-] Agent initialized successfully, now running...
2018-02-07 16:13:37.109 16827 INFO neutron.plugins.ml2.drivers.agent._common_agent [req-c5f31199-1bd8-43e0-be74-7fed526211ff - - - - -] RPC agent_id: lb58ac785a22fe
2018-02-07 16:13:37.126 16827 INFO neutron.agent.agent_extensions_manager [req-c5f31199-1bd8-43e0-be74-7fed526211ff - - - - -] Loaded agent extensions: []
2018-02-07 16:13:37.428 16827 INFO neutron.plugins.ml2.drivers.agent._common_agent [req-c5f31199-1bd8-43e0-be74-7fed526211ff - - - - -] Linux bridge agent Agent RPC Daemon Started!
2018-02-07 16:13:37.429 16827 INFO neutron.plugins.ml2.drivers.agent._common_agent [req-c5f31199-1bd8-43e0-be74-7fed526211ff - - - - -] Linux bridge agent Agent out of sync with plugin!
2018-02-07 16:13:37.637 16827 INFO neutron.plugins.ml2.drivers.linuxbridge.agent.arp_protect [req-c5f31199-1bd8-43e0-be74-7fed526211ff - - - - -] Clearing orphaned ARP spoofing entries for devices []