Add a provison-step on failing host config autodetect

After all autodetect options for host configuration failed, stboot should prepare for provisioning. Provisioning is done via a usual OS pkg which can be put inside the initramfs.

So, the provisioning step must manipulate the former read trust policy so that the OS pkg fetching method is set to "initramfs" and create a valid minimal host configuration that contains a well-known path to the OS pkg inside the initramfs.