Start the working threads:

    - Health monitor (the health plugin)
    - Config change monitor (the watcher plugin)

def start_plugins(conf, watcher_plugin_class, health_plugin_class,
                  sleep_time):
    """
    Start the working threads:

    - Health monitor (the health plugin)
    - Config change monitor (the watcher plugin)

    """
    # No matter what the chosen plugin to watch for config updates: We get a
    # plugin-handle back. This gives us a start(), stop() and
    # get_route_spec_queue() function. All watcher plugins provide the same
    # interface.
    watcher_plugin = watcher_plugin_class(conf)
    watcher_plugin.start()

    # Similarly for the health-monitor-plugin. It gives us a get_queues()
    # function, to get the monitor-ips and failed-ips queues.
    health_plugin = health_plugin_class(conf)
    health_plugin.start()

    return watcher_plugin, health_plugin