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.

The problem is that ```PowerManager::BMC.new(smart_proxies(:bmc))``` tries to reach the smart proxy and fails. Tries to stub that, without success, which is why I did the power mocker.