installer - Fix a bug in survey_storage()
- survey_storage() issues DIOCGPART on every disk present in
kern.disks in order to retrieve information about it.
The problem was that a failure to get that information from
any disk in the list caused the whole storage survey to be
marked as failed. This happens, for example, with some card
readers that present the disk devices even though there is no
media inserted on the corresponding slot.
- Fix the logic in the installer and allow to check all disks
in the system.