code: def QA_user_sign_up(name, password, client):
      
  
      coll = client.user
      if (coll.find({'username': name}).count() > 0):
          print(name)
          QA_util_log_info('user name is already exist')
          return False
      else:
          return True
docs: 只做check! 具体逻辑需要在自己的函数中实现
  
      参见:QAWEBSERVER中的实现
      
      Arguments:
          name {[type]} -- [description]
          password {[type]} -- [description]
          client {[type]} -- [description]
      
      Returns:
          [type] -- [description]