Fixes #746 - Generate all the Host template when click on Build to avoid...

Generate all the Host template when click on Build to avoid errors during installation.
Includes moving of template_used to Managed model so it can be used elsewhere.

you can avoid returning self if you change this line to
```ruby
(@build = HostBuildStatus.new(@host)).host_build_status
```

another simple way, is to add a method on the host object similar to
```ruby
def build_status
  build_status = HostBuildStatus.new(self)
  build_status.host_build_status # I would rename to method but thats another story
  build_status
end
```