fixes #6226 - if only one option for required field on new host page (ex. installation media), then automatically select it

The problem is that the noun doesn't get translated as it is... you want to be able to say "Choisir un environnement" rather than "Choisir un environment", and it touches upon an issue that's seen in the UI in a few other places, that concatenating strings like this isn't i18n-friendly (e.g. in that example, the gender of the noun varies, so doesn't make sense to translate "Select %s" to "Select un".)

Really I think these strings would need to be generated in full into locale/model_attributes.rb or similar so they can be translated in their entirety, instead of using humanize and concatenation.