fix: pass pytest xmodule SplitTestBlockLMSTest

[Carlos-Muniz]

As part of #36, several tests have been discovered that are not passing in tutor, but passing in devstack. The following tests may not be run by tutor, or may be failing in tutor.

xmodule/tests/test_split_test_module.py::SplitTestBlockLMSTest::

• test_child_1__0___split_test_cond0__
• test_child_2__1___split_test_cond1__
• test_child_missing_tag_value_1_0
• test_child_missing_tag_value_2_1
• test_child_persist_new_tag_value_when_tag_missing_01_100
• test_child_persist_new_tag_value_when_tag_missing_02_200
• test_child_persist_new_tag_value_when_tag_missing_03_300
• test_child_persist_new_tag_value_when_tag_missing_04_400
• test_child_persist_new_tag_value_when_tag_missing_05_500
• test_child_persist_new_tag_value_when_tag_missing_06_600
• test_child_persist_new_tag_value_when_tag_missing_07_700
• test_child_persist_new_tag_value_when_tag_missing_08_800
• test_child_persist_new_tag_value_when_tag_missing_09_900
• test_child_persist_new_tag_value_when_tag_missing_10_1000
• test_export_import_round_trip
• test_get_html_1__0___HTML_FOR_GROUP_0__
• test_get_html_2__1___HTML_FOR_GROUP_1__

For more information about the tests that passed, failed, skipped, or never ran, see the spreadsheet with all the tests.

[Carlos-Muniz]

This test(s) does pass in tutor. See #155 for more details.