tools: support testing known issues

This commit adds a known_issues directory to the test directory
for scripts that reproduce known bugs. Since these scripts are
expected to fail, it also adds a --expect-fail flag to test.py
which reports tests as successful when they fail.

Refs: https://github.com/nodejs/testing/issues/18
PR-URL: https://github.com/nodejs/node/pull/5528


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Wyatt Preul <wpreul@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>