Add transaction for setting agent_id in L3HARouterAgentPortBinding
Add transaction for setting agent_id in L3HARouterAgentPortBinding

To avoid having extra L3HARouterAgentPortBinding with l3_agent as
None, operation of setting l3_agent should be atomic.
For this purpose, transaction was added in methods
create_ha_port_and_bind and _bind_ha_router_to_agents.

Closes-Bug: #1499647

Change-Id: Iaad82fe522cfd70061daecf411c924fdc11b7e41
chitr/neutron,mahak/neutron,cloudbase/neutron,wolverineav/neutron,openstack/neutron,dims/neutron,huntxu/neutron,igor-toga/local-snat,klmitch/neutron,apporc/neutron,igor-toga/local-snat,klmitch/neutron,MaximNevrov/neutron,sebrandon1/neutron,mahak/neutron,mahak/neutron,sebrandon1/neutron,huntxu/neutron,eayunstack/neutron,noironetworks/neutron,bigswitch/neutron,openstack/neutron,chitr/neutron,noironetworks/neutron,apporc/neutron,wolverineav/neutron,MaximNevrov/neutron,bigswitch/neutron,dims/neutron,cloudbase/neutron,eayunstack/neutron,openstack/neutron