Fix unit test failure due to stale urls.py
Merge pull request #6273 from edx/renzo/fix-shoppingcart-tests

Fix unit test failure due to stale urls.py
Positive filtering which steps can be skipped.
Merge pull request #6272 from edx/sanchez/change-skip-step-logic

Positive filtering which steps can be skipped.
Return empty values and log a warning instead of raising NotImplemented
exceptions for XML modulestore asset metadata methods.
Export modulestore-stored asset metadata as XML to exported course.
Import asset metadata XML into modulestore.
Optimize importing many items of asset metadata by avoiding multiple
round-trips to MongoDB.
Add wrapper class that enables storage of Mongo document id separately
from dictionary of all asset metadata by asset type.