Right now the mock build go into the default directory
/var/lib/mock/...

It would be trivial to add "--resultdir=..." to the mock command. I'm
thinking it could either go directly in the bug directory, ~/ or
perhaps in a sub-directory, ~//build_results or something like
that. That way when they're done with the review a simple rm -rf
~/ gets everything. And running fedora-review on another bug doesn't clean up the results of the preview review prematurely.