Importable python_lib.zip assets

Lots of plumbing to allow an asset named python_lib.zip to be imported
by jailed Python code.

This function can find the "python_lib.zip" asset, and is passed down
through ModuleSystem and LoncapaSystem so that capa problems have access
to the zipfile.

lms/djangoapps/courseware/module_render.py

@@ -35,6 +35,7 @@ from xblock.django.request import django_to_webob_request, webob_to_django_respo
 from xmodule.error_module import ErrorDescriptor, NonStaffErrorDescriptor
 from xmodule.exceptions import NotFoundError, ProcessingError
 from opaque_keys.edx.locations import SlashSeparatedCourseKey
+from xmodule.contentstore.django import contentstore
 from xmodule.modulestore.django import modulestore, ModuleI18nService
 from xmodule.modulestore.exceptions import ItemNotFoundError
 from xmodule.util.duedate import get_extended_due_date
@@ -50,7 +51,7 @@ from xmodule.lti_module import LTIModule
 from xmodule.x_module import XModuleDescriptor
 
 from util.json_request import JsonResponse
-from util.sandboxing import can_execute_unsafe_code
+from util.sandboxing import can_execute_unsafe_code, get_python_lib_zip
 
 
 log = logging.getLogger(__name__)
@@ -530,6 +531,7 @@ def get_module_system_for_user(user, field_data_cache,
         s3_interface=s3_interface,
         cache=cache,
         can_execute_unsafe_code=(lambda: can_execute_unsafe_code(course_id)),
+        get_python_lib_zip=(lambda: get_python_lib_zip(contentstore, course_id)),
         # TODO: When we merge the descriptor and module systems, we can stop reaching into the mixologist (cpennington)
         mixins=descriptor.runtime.mixologist._mixins,  # pylint: disable=protected-access
         wrappers=block_wrappers,