(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.
Heh, I'm not really sure now that I really look at it. Maybe it my head this was an installer test? I'll make it something more logical.