Reusing downloaded packages for multiple system-upgrades

[Sam Varshavchik]

With prior releases, I saved a bunch of bandwidth with system-upgrading  
multiple machines by stashing away a copy of the downloaded  
/var/lib/dnf/system-upgrade, and then copying it to the remaining boxes  
upfront. That directory was just a flat directory, containing the downloaded  
rpms, and their system-upgrades simply saw that most of the stuff was  
already downloaded.

Looks like in F27, /var/lib/dnf/system-upgrade is an entire directory  
structure, and each repository's packages are stashed away in subdirectory  
that are tagged with the repository's current version tag.

What's the best way to minimize downloads now? I could make a copy of the  
entire /var/lib/dnf/system-upgrade structure, but I will be rolling the  
upgrades over the course of several days, during which I expect all the  
update repos to be updated as usual, with their version tags changing.