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.

can you wrap the rescue just around the host.power actions? i would hope / assume all other exceptions are handled.
also you catching the exception and ignoring, most likely it needs to be logged and reported somewhere in the UI too?