Switch to using concat{} instead of lots of file{} magic.

WARNING:  I based this off my apt branch so that would ideally be merged first to clean up the diff on this.
WARNING:  These commits mean vhosts get created in /etc/nginx/conf.d/$name.conf instead of a single file.

I'm making this as it's almost ready to be merged but I wanted to open one thing to discussion first.  Should I automatically delete autogen.conf as part of these changes so that you don't end up with duplicate entries or would you prefer that users do that themselves?

I lean towards a new file{} for autogen that deletes the existing file as part of this but I wanted to open it to the floor.