test: switch default test store to the split store

It's long past time that the default test modulestore was Split,
instead of Old Mongo. This commit switches the default store and
fixes some tests that now fail:
- Tests that didn't expect MFE to be enabled (because we don't
  enable MFE for Old Mongo) - opt out of MFE for those
- Tests that hardcoded old key string formats
- Lots of other random little differences

In many places, I didn't spend much time trying to figure out how to
properly fix the test, and instead just set the modulestore to Old
Mongo.

For those tests that I didn't spend time investigating, I've set
the modulestore to TEST_DATA_MONGO_AMNESTY_MODULESTORE - search for
that string to find further work.

lms/djangoapps/grades/tests/integration/test_problems.py

@@ -5,6 +5,14 @@ import itertools
 import ddt
 import pytz
 from crum import set_current_request
+from xmodule.graders import ProblemScore
+from xmodule.modulestore import ModuleStoreEnum
+from xmodule.modulestore.tests.django_utils import (
+    TEST_DATA_MONGO_AMNESTY_MODULESTORE, ModuleStoreTestCase, SharedModuleStoreTestCase,
+)
+from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory
+from xmodule.modulestore.tests.utils import TEST_DATA_DIR
+from xmodule.modulestore.xml_importer import import_course_from_xml
 
 from capa.tests.response_xml_factory import MultipleChoiceResponseXMLFactory
 from common.djangoapps.student.models import CourseEnrollment
@@ -12,12 +20,6 @@ from common.djangoapps.student.tests.factories import UserFactory
 from lms.djangoapps.course_blocks.api import get_course_blocks
 from lms.djangoapps.courseware.tests.test_submitting_problems import ProblemSubmissionTestMixin
 from openedx.core.djangolib.testing.utils import get_mock_request
-from xmodule.graders import ProblemScore  # lint-amnesty, pylint: disable=wrong-import-order
-from xmodule.modulestore import ModuleStoreEnum  # lint-amnesty, pylint: disable=wrong-import-order
-from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase, SharedModuleStoreTestCase  # lint-amnesty, pylint: disable=wrong-import-order
-from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory  # lint-amnesty, pylint: disable=wrong-import-order
-from xmodule.modulestore.tests.utils import TEST_DATA_DIR  # lint-amnesty, pylint: disable=wrong-import-order
-from xmodule.modulestore.xml_importer import import_course_from_xml  # lint-amnesty, pylint: disable=wrong-import-order
 
 from ...subsection_grade_factory import SubsectionGradeFactory
 from ..utils import answer_problem, mock_get_submissions_score
@@ -28,6 +30,7 @@ class TestMultipleProblemTypesSubsectionScores(SharedModuleStoreTestCase):
     """
     Test grading of different problem types.
     """
+    MODULESTORE = TEST_DATA_MONGO_AMNESTY_MODULESTORE
 
     SCORED_BLOCK_COUNT = 7
     ACTUAL_TOTAL_POSSIBLE = 17.0
@@ -102,6 +105,8 @@ class TestVariedMetadata(ProblemSubmissionTestMixin, ModuleStoreTestCase):
     Test that changing the metadata on a block has the desired effect on the
     persisted score.
     """
+    MODULESTORE = TEST_DATA_MONGO_AMNESTY_MODULESTORE
+
     default_problem_metadata = {
         'graded': True,
         'weight': 2.5,
@@ -210,6 +215,7 @@ class TestWeightedProblems(SharedModuleStoreTestCase):
     """
     Test scores and grades with various problem weight values.
     """
+    MODULESTORE = TEST_DATA_MONGO_AMNESTY_MODULESTORE
 
     @classmethod
     def setUpClass(cls):