def expunge(self, instance):
        instance = self.pop(instance)
        instance.session = None
        return instance
From the given list of volumes, find volumes created by tests which are
dataset/ETHPy150Open lsbardel/python-stdnet/stdnet/odm/session.py/SessionModel.expunge--crossover with--dataset/ETHPy150Open ClusterHQ/flocker/admin/cleanup.py/CleanVolumes._filter_test_volumes