code: def modify_password(self, username, newpwd, oldpwd):
          
          ret = self.command(
              'userManager.cgi?action=modifyPassword&name={0}&pwd={1}'
              '&pwdOld={2}'.format(username, newpwd, oldpwd)
          )
          return ret.content.decode('utf-8')
docs: Params:
              username - user name
              newpwd - new password
              oldpwd - old password