WIP: Support for copying the OS to USB drives
This builds on (and is based on) !217 (which is, in turn, based on !216) to add the framework for copying the OS to a USB drive. This is designed for OSTree-based OSs (such as EOS) to allow OS updates to be copied between computers without using the internet.
It just adds the relevant vfuncs and UI — the implementation of copying the OSTree repository would be added to an EOS-specific plugin (probably the
eos-updater plugin being added in !197 (merged)) and I’m not going to propose that for review until all this is reviewed and (hopefully) merged.
It was mostly written by Travis Reitter and @mwleeds, with some tweaks and rearrangement done by me when rebasing it for upstreaming.