Create snapshot for list of volumes
        :param systemID: Cluster ID 
        :param snapshotSpecificationObject: Of class SnapshotSpecification
        :rtype: SnapshotGroupId

def create_snapshot(self, systemId, snapshotSpecificationObject):
        """
        Create snapshot for list of volumes
        :param systemID: Cluster ID 
        :param snapshotSpecificationObject: Of class SnapshotSpecification
        :rtype: SnapshotGroupId
        """
        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