Install Flag for Pre-Installed Diamond

We are creating our OS images with every software products that we need are pre-installed. Then we use vagrant, which uses puppet to configure those software products. If we use the diamond package as is, we get duplicate declaration errors. That's why I introduced an install flag to skip the installation and just use the configuration. I think this change might be useful to other people as well.

Cheers,

Sercan Aktas
I'd maybe name this something a bit more explicit, like `manage_installation`