Sometime during the 2.x's, `at_exit` changed its ordering. As a result,
a lot of things that were stacking `at_exit`'s broke. This is one of
those since both simplecov and minitest do their thing via `at_exit`.
This switches to simplecov w/ no defaults on, then replicates their
simplecov/defaults.rb with our own.
I'm going to try to get that entire file back upstream but it can live
here for now.
Signed-off-by: Ryan Davis <zenspider@chef.io>
