Workaroud to fix slow agents

With this configuration we are instructing the quantum-server to not consider an agent down until 3 report_state are not received from this agent, this will fix specially the dhcp configuration that we had a lot of problem with recently which due to the fact that some rpc calls (port_creation, port_deletion) are not sent because quantum-server think that the dhcp-agent is down, as for why dhcp-agent does not send report state in time that a story for another time :).