'Add new server to the group.'

def AddServer(self, addr, port):

    server = DataServer(('http://%s:%d' % (addr, port)), len(self.servers))
    self.servers.append(server)
    server.SetInterval(constants.MAX_RANGE, constants.MAX_RANGE)
    self.mapping.servers.Append(server.GetInfo())
    self.mapping.num_servers += 1
    return server
