add data_dir to bok_choy test settings

cms/envs/bok_choy.py

@@ -39,6 +39,7 @@ INSTALLED_APPS += ('django_extensions',)
 TEST_ROOT = REPO_ROOT / "test_root"  # pylint: disable=no-value-for-parameter
 GITHUB_REPO_ROOT = (TEST_ROOT / "data").abspath()
 LOG_DIR = (TEST_ROOT / "log").abspath()
+DATA_DIR = TEST_ROOT / "data"
 
 # Configure modulestore to use the test folder within the repo
 update_module_store_settings(