Add way to grab stdout from within test

[racoltdev]

[racoltdev]

I should just be able to expose a func that reads pipe and returns a malloc string. The only caveat is that test_builder would have to store a little state about this read string so it could still log it and not attempt to reread from the pipe. Or maybe this call should act like clearing stdout, and msgs already read are not reported?

Marking low priority since meta tests/test suites should be able to cover this use case for the most part.