solbuild init fails if /var/lib/solbuild/images/$repo-x86_64.img.xz out of date

[TraceyC77]

Recently I ran into an issue where running solbuild init failed. This was after the outage.
The error was that it failed to decompress the downloaded file.
The file that was downloaded was a 404 page in html rather than the tarball because the file /var/lib/solbuild/images/unstable-x86_64.img.xz pointed to a resource that was no longer available

The manual workaround was to delete /var/lib/solbuild/images/unstable-x86_64.img.xz and run the command again

Proposed solution: Add logic to solbuild init that if it gets an error trying to uncompress the repo archive, that it offers the user an action to fix (delete the bad tarball).

Logic flow:

When running solbuild init
If an error is encountered when trying to decompress the downloaded repo archive file
Check /var/lib/solbuild/images for a pre-existing file like unstable-x86_64.img.xz
Check if that file is valid. If not:
Offer user to delete that file,

If user chooses no, exit with warning that things may still be bork
If yes, delete that file. Rerun solbuild init, check for success.

[TraceyC77]

Wrong tracker. Filed at getsolus/solbuild#29