This reverts commit 9967b6fd.

We're seeing errors in NR from objects read out of the cache lacking the
'StaticContent' object has no attribute 'content_digest'
File "/edx/app/edxapp/edx-platform/common/djangoapps/contentserver/middleware.py",
    line 70, in process_request

This reverts commit 849ebc5f.

Instead, use a class attribute to define test behavior. This allows for
easier addition of new mixins over time.

The existing pattern of using `override_settings(MODULESTORE=...)` prevented
us from having more than one layer of subclassing in modulestore tests.

In a structure like:

    @override_settings(MODULESTORE=store_a)
    class BaseTestCase(ModuleStoreTestCase):
        def setUp(self):
            # use store

    @override_settings(MODULESTORE=store_b)
    class ChildTestCase(BaseTestCase):
        def setUp(self):
            # use store

In this case, the store actions performed in `BaseTestCase` on behalf of
`ChildTestCase` would still use `store_a`, even though the `ChildTestCase`
had specified to use `store_b`. This is because the `override_settings`
decorator would be the innermost wrapper around the `BaseTestCase.setUp` method,
no matter what `ChildTestCase` does.

To remedy this, we move the call to `override_settings` into the
`ModuleStoreTestCase.setUp` method, and use a cleanup to remove the override.
Subclasses can just defined the `MODULESTORE` class attribute to specify which
modulestore to use _for the entire `setUp` chain_.

[PLAT-419]

This feature allows upload of video assets to S3. This requires that the
VIDEO_UPLOAD_PIPELINE setting be properly configured and that each
course be configured with a token issued by the media team for their
processing purposes (e.g. linking the video with a YouTube channel).

Co-authored-by: Greg Price <gprice@edx.org>

Move modulestore config for tests to an importable location
Disable pylnt warning for lms imports in common tests
Refactor all testcases that loaded all xml courses
TE-610
TE-489

TE-489

add test for videomodule

Import drafts handles modules w/o xml_attributes
and ones using the old parent_sequential_url pointer

Handle drafts for modules which don't define nor extract xml_attributes

Support  and  in get_items qualifiers

Unit test for   value query

LMS-11437

LMS-11213

LMS-11210

Conflicts:
	common/lib/xmodule/xmodule/modulestore/split_mongo/split_draft.py

STUD-1726

Conflicts:
	cms/djangoapps/contentstore/tests/test_course_listing.py

Added update_item, create_item, create_child to split_draft.py

Cleaned up TODOs in test_mixed_modulestore.py

Unit test for auto-publish

LMS-11017

Added tests to test_mixed_modulestore.py for has_changes and added black_list to _auto_publish

Moved DIRECT_ONLY_CATEGORIES to draft_and_publish.py

Deleted test_split_draft_modulestore.py

Added _auto_publish to create course

Publish cleanups for update_version, source_version

Changed has_changes to use source_version

Removing mixed test that no longer makes sense in auto_publish world

Addressed TODOs in test_branch_setting