Issue:
When using Open vSwitch HWVTEP Emulator (L2GW Node), part of L2GW CONNECTION operation may not be reflected after stop one ODL node in a 3 node ODL cluster.
Specifically, in some cases the tunnel to L2GW Node may not be created in Controller Node.

Occurrence rate:
3/12 times

Reproduction steps:
1. Start 3 node ODL cluster
2. Set OVS of Controller/Compute/L2GW(HWVTEP Emulator)
3. Create Network
4. Create L2 GATEWAY
5. Create L2 CONNECTION
Confirm Logical Switch is created
Confirm Logical Switch flows are created correctly
Confirm Physical Switch flows are created correctly
Confirm the tunnel to L2GW Node is created in Controller Node
6. Stop one ODL node
7. Delete the L2 CONNECTION created in step 5
Confirm Logical Switch is deleted
Confirm Physical Switch flows is deleted
8. Delete L2 GATEWAY created in step 4
Confirm the tunnel to L2GW Node is deleted in Controller Node
9. Create L2 GATEWAY (new)
10. Create L2 CONNECTION (new)
Confirm Logical Switch is created
Confirm Logical Switch flows are created correctly
Confirm Physical Switch flows are created correctly
*Confirm the tunnel to L2GW Node is NOT created in Controller Node

Environment Details:
OpenStack: stable/ocata
ODL: carbon-SR1
features: odl-netvirt-openstack odl-neutron-hostconfig-ovs odl-mdsal-apidocs
Node:
OpenStack Controller Node: 1 Node
OpenStack Compute Node: 1 Node
ODL Node: 3 Nodes
L2GW Node: 1 Node

Questions:

• There is only one OpenFlow session in L2GW Node, is it correct?
  In L2GW Node, we executed the following command:
  "vtep-ctl set-manager tcp: {ODL1}:6640 tcp:{ODL2}:6640 tcp:{ODL3}:6640"
  We found that there are three OVSDB sessions(one session for each ODL Node),
  but only one OpenFlow session connecting with one of the three nodes.
  In Controller Node and Compute Node, we executed the following command:
  "ovs-vsctll set-manager tcp:{ODL1}

  :6640 tcp:

  {ODL2}:6640 tcp:{ODL3}:6640"
  We found that there are three OVSDB sessions(one session for each ODL Node),
  and three OpenFlow session connecting to each ODL node.
  
  - The Controller IP of L2GW Node is shown as VIP, is it correct?
  We also tried execute set-manager command after assigned VIP to ODL cluster.
  By checking the result of 'ovs-vsctl show' command,
  We found in L2GW Node it shows:
  Controller "tcp:{VIP}:6653"
  but in Controller Node and Compute Node it shows:
  Controller "tcp:{ODL1}:6653"
  Controller "tcp:{ODL2}

  :6653"
  Controller "tcp:

  {ODL3}

  :6653"