test: make test runner multi-arch/mode compatible

Make `python tools/test.py --arch=ia32,x64 --mode=debug,release` work.
The test runner looks for the `node` binary in `out/${arch}.${mode}/`.

Running tools/test.py without --arch makes it use `out/Release/node` or
`out/Debug/node` like before.

This commit removes `test/simple/test-executable-path.js` because the
assumptions it makes about the locations of the debug and release
binaries are now outdated.

PR-URL: https://github.com/node-forward/node/pull/24


Reviewed-By: Fedor Indutny <fedor@indutny.com>