Fix cmd.exe tests

[jonashaag]

Reproducer for #39

[wolfv]

I think we need to check the %errorlevel%:

e.g.

if %errorlevel% neq 0 exit /b %errorlevel%

that should propagate the error properly

[jonashaag]

Thanks for the pointer, I wanted to avoid copy-pasting that a dozen times...

[jonashaag]

Why does it stop executing the cmd.exe commands? I thought there was no fail-fast in cmd.exe.

[jonashaag]

@tdegeus if you have time to investigate the bug source of the bug that would be great!