neutron-sriov-nic-agent cannot be disabled

[Eduardo Olivares]

During a test, neutron-sriov-nic-agent was disabled (openstack network agent set --disable <agent-id>) and then some operations that require the intervention of this agent were successfully performned. So, apparently the agent is not really disabled, despite showing state=DOWN.

Please see the bug reproduction here:
http://paste.openstack.org/show/797088/

Apparently, only DHCP and L3 agents receive the status flag. In other words: only those two agents are capable of being enabled or disabled: https://github.com/openstack/neutron/blob/master/neutron/db/agentschedulers_db.py#L53-L56

Maybe the API should answer the --disable request with an error, instead of 200 OK.