Ensure dhclient is not restarted if configuration does not change

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>
go agent sends heartbeat over nats every minute
Extract convert_old_message_to_new out of AgentClient

Signed-off-by: Jesse Zhang <jz@pivotallabs.com>
remove default value for event_ticker in instance_updater

it was never omitted except for in tests