set floatingip status to DOWN during creation

[venkata anil]

floatingip status is not reliable as it is set to active during creation itself [1] rather than waiting for agent [2] to update it once agent finishes adding SNAT/DNAT rules.
[1] https://github.com/openstack/neutron/blob/master/neutron/db/l3_db.py#L1234
[2] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/agent.py#L131

User can check floatingip status after creation and can initiate data traffic before agent finishes
 processing floatingip resulting in connection failures. Also fixing this can help tempest tests to initiate connection only after agent has finished floatingip processing and avoid failures.

Also floatingip status has to be properly updated during migration of router.