(PUP-2912) PMT Build symlink exception

Prior to this commit the build command would add symlinks to packages. This
can cause unexpected behavior when installed on a system.
This commit causes the build command to throw an error when it finds a symlink.
That should prevent new modules from being created with a symlink included.
I think this is supposed to be the same as above...
File.join(path, "pkg", "#{module_name}-#{version}", file)
In that I think you're seeing that this file doesn't exist, but it doesn't exist because it's not supposed to exist.