witadmin.exe path issues

[HamsterExAstris]

There are two separate issues with the path logic.

1. When witadmin.exe is in the path, Test-Path will fail, so it will still throw even though it's valid and can do the work.

2. In 32-bit PowerShell processes, $env:ProgramFiles resolves to C:\Program Files (x86), so $VSDirectories is built with the wrong path.