Code review comment for lp://staging/~nataliabidart/software-center/fix-977931

Thanks Natalia for this branch and sorry for my slow reply.

First let me say thanks for the work and the refactor and the excellent test, we shall use that
as a example.

This looks fine, there have been some changes in the 5.2 branch so I merged it and resolved
conflicts and tweaked it a bit more, please remerge lp:~mvo/software-center/fix-977931/ with this branch
and let me know what you think.

I was curious how to reproduce/understand the changes in appview.py, reviews.py that cause the model to
be "None". I revert that change but for me its not crashing so I wonder if that is still needed? Or is it
a random issue? Except for this (which I just would like to understand better how it happens) the branch
is +10 approve ;)

Additional thanks for unifying get_mock_options() and the with open() fix (and the cleanup) in test_database.py.