Move helper modules outside of tests directory and namespace them with rt_

[andrewjstone]

It's confusing when I see things like repl_util:blah(). I assume that function is part of repl, instead of included in the tests directory. It'd be nice if these util modules could live under src or in a modules directory or something.

[cmeiklejohn]

Yes, I agree. We need to reorganize the helpers.