Add DEFAULT_FILE_STORAGE configuration.

Tests in common are run with both CMS and LMS configuration (with different env files). Ensure the DEFAULT_FILE_STORAGE variables are in both environments.

cms/envs/test.py

@@ -19,7 +19,8 @@ from warnings import filterwarnings, simplefilter
 from uuid import uuid4
 
 # import settings from LMS for consistent behavior with CMS
-from lms.envs.test import (WIKI_ENABLED, PLATFORM_NAME, SITE_NAME)
+# pylint: disable=unused-import
+from lms.envs.test import (WIKI_ENABLED, PLATFORM_NAME, SITE_NAME, DEFAULT_FILE_STORAGE, MEDIA_ROOT, MEDIA_URL)
 
 # mongo connection settings
 MONGO_PORT_NUM = int(os.environ.get('EDXAPP_TEST_MONGO_PORT', '27017'))