Updated rspec syntax and spree namespacing for readability.

Did this in #2770 that I closed due to that I went rampage with code formatting on that one :)

- Rspec expect syntax instead of lambda and other rspec syntax changes for nil and boolean comparison.
- Added Spree namespace to models without removing nested `module` due to that `git` mark all code as modified, so I leave that to the core team to clean up when desired.
- Removed forgotten FactoryGirl cleanups that was done earlier in an already merged commit.