def clean(self, stall_time=None):
        self.reap_invalid()

        if stall_time is None:
            stall_time = self.conf.image_cache_stall_time

        self.reap_stalled(stall_time)
manage.py validate reports an error on a non-existent app in INSTALLED_APPS
dataset/ETHPy150Open rcbops/glance-buildpackage/glance/image_cache/drivers/xattr.py/Driver.clean--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/tests/regressiontests/admin_scripts/tests.py/ManageValidate.test_nonexistent_app