Manifest-db uses a lot of duplicated UUIDs which will cause CI problems

[mvo5]

We get regular failures in the manifest-db run. With the extra visibility from #123 it seems the errors we get (sometimes) are related to an xfs mount

mount/- (org.osbuild.xfs): mounting /dev/98302bc3-1aa3-4eab-96e9-9f1c6eb539ce/rootlv -> /var/lib/osbuild/store/tmp/buildroot-tmp-3y2wyhos/mounts/
mount/- (org.osbuild.xfs): already unmounted: /var/lib/osbuild/store/tmp/buildroot-tmp-3y2wyhos/mounts/

which looks similar the UUID clashes we observed in osbuild/osbuild#1641

I opened various PRs to fix this, I'm not sure (yet) if I have the complete picutre of all the moving pieces from manifest DB and some (all?) may need rework or closing so decided to use this issue to keep track:

• manifest-db: make all UUIDs unique #124
• gen-manifests: derive seedArg from filename and env images#664
• cmd: add helper for seed generation images#674