code: def member_update(self, repl_id, member_id, params):
          
          repl = self[repl_id]
          result = repl.member_update(member_id, params)
          self[repl_id] = repl
          return result
docs: apply new params to replica set member
          Args:
              repl_id - replica set identity
              member_id - member index
              params - new member's params
  
          return True if operation success otherwise False