title: Add new host to a running txloadbalancer
body: <p>I am using txloadbalancer twisted API in my application and it works great. I have one problem tho, I can't figure out a way too add hosts to a running instance.</p>
  
  <p>I use this function for now:</p>
  
  <pre><code>#pm is a ProxyManager
  def addServiceToPM(pm, service):
      if isinstance(service, model.HostMapper):
          [service] = model.convertMapperToModel([service])
      for groupName, group in pm.getGroups(service.name):
          proxiedHost = service.getGroup(groupName).getHosts()[0][1]
          pm.getGroup(service.name, groupName).addHost(proxiedHost)
          tracker = HostTracking(group)
          scheduler = schedulers.schedulerFactory(group.lbType, tracker)
          pm.addTracker(service.name, groupName, tracker)
  </code></pre>
  
  <p>and run it with a new host</p>
  
  <pre><code>addServiceToPM(pm, HostMapper(proxy='127.0.0.1:8080', lbType=roundr,
                 host='host2', address='127.0.0.1:10002'))
  </code></pre>
  
  <p>This adds the host correctly to the tracker, but not to the proxy service and it is thus not used in the load balancing. Do anyone have a clue about how to do this?</p>