code: def create_snapshot(self, systemId, snapshotSpecificationObject):
          
          self.conn.connection._check_login()
          #try:
          response = self.conn.connection._do_post("{}/{}{}/{}".format(self.conn.connection._api_url, "instances/System::", systemId, 'action/snapshotVolumes'), json=snapshotSpecificationObject.__to_dict__())
          #except:
          #    raise RuntimeError("create_snapshot_by_system_id() - Error communicating with ScaleIO gateway")
          return response
docs: Create snapshot for list of volumes
          :param systemID: Cluster ID 
          :param snapshotSpecificationObject: Of class SnapshotSpecification
          :rtype: SnapshotGroupId