Exit after dummy app cannot be found
Only load accessible driver if asked to do so
Only skip capybara inaccessible specs if accessible driver is loaded
Defaulting variant weight to 0 at the schema level

Fixes #4300
Fixes #4311
ReturnAuthorization uses stock_location_id

- Replaced code in ReturnAuthorization#process_return to find the
  StockItem based on ReturnAuthorization#stock_location_id rather than the
  original shipment's stock location.
- Modified feature and controller specs to set the stock_location_id
- Added tests to the return authorization model specs that test
  returning to either the initial stock location or a new stock
  location. These currently fail (by design).
Use correct response.body in set_jsonp_format

Fixes #4332
[api] Use order.contents.remove to remove line items from orders
Call ensure_updated_shipments on line items destroy

We also need to call ensure_updated_shipments when a line item is destroyed.

Fixes #4325