Allow site preparation without installation.

I think we need to finally address this "aegirism": You can't get a site working in aegir without a successful install or clone.

Reasoning:

• Drupal 8's install wizard is beautiful and useful. It's a shame we can't let users use that to setup their sites. I just walked through the free drupal 8 site setup with Acquia and Pantheon and it is an amazing experience.
• There are more and more install profiles out there with increasingly complex install wizards. We should be able to support those projects without writing a ton of extra code in hostmaster.
• It is simply more intuitive. When install and clone tasks fail and the site does not exist at all as a result, the impression is that the platform (not the node type) is broken, when the errors exist in the application.
• This is a blocker toward being more general purpose, allowing for basic VHOST setup, static site hosting, or other apps hosting like wordpress.

I'm marking this as major because I see this a major blocker toward the growth of the aegirproject.