Fix Django Contrib Site broken cache in tests
Fix Django Contrib Site broken cache in tests

When tests were run for the first time, right after migrations finished,
the cache for sites contained fake item. It prevented using
`get_current`, because `get_current` looks up the cache. Therefore
any code using `Site.objects.get_current()` for a ForeignKey would end
up broken.

The only fast & feasible way of fixing this behavior that I came up with
was to reset the cache in base test.

pbanaszkiewicz/amy,pbanaszkiewicz/amy,pbanaszkiewicz/amy,swcarpentry/amy,swcarpentry/amy,swcarpentry/amy