docs: def update(self, volume_id, **kwargs):
          """
          update an export
          """
          # These arguments are allowed
          self.allowed('update', kwargs,
                       ['status', 'instance_id',
                        'mountpoint', 'ip', 'initiator', 'session_ip',
                        'session_initiator'])
          # Remove parameters that are None
          params = self.unused(kwargs)
          return self.http_post('/volumes/%s/export' % volume_id, params=params)