Improve fallbacks if no disks or no adapters
Improve fallbacks if no disks or no adapters

* Fallback to `generate_ethernet_pc_id` if there are no disks.
* Fallback to `generate_disk_pc_id` if there are no adapters.

See details in #25

Closes: #25

open-license-manager/open-license-manager,open-license-manager/open-license-manager