Avoid using real data for tests

[adborden]

Currently most of our tests uses real data for test setup

disclosure-backend/finance/tests/test_xformnetfilerawdata.py

Line 28 in 9abb457

call_command('xformnetfilerawdata',

This makes the tests inconsistent from run to run and make them prone to breakage based on changes to production code. I'd prefer to mock this data out or use fixtures.