code: def member_command(self, member_id, command):
          
          server_id = self._servers.host_to_server_id(
              self.member_id_to_host(member_id))
          return self._servers.command(server_id, command)
docs: apply command (start/stop/restart) to member instance of replica set
          Args:
              member_id - member index
              command - string command (start/stop/restart)
  
          return True if operation success otherwise False