code: def member_command(self, repl_id, member_id, command):
          
          repl = self[repl_id]
          result = repl.member_command(member_id, command)
          self[repl_id] = repl
          return result
docs: apply command(start, stop, restart) to the member of replica set
          Args:
              repl_id - replica set identity
              member_id - member index
              command - command: start, stop, restart
  
          return True if operation success otherwise False