aptly: Change snapshot distro/prefix to match reprepro
requested to merge adalessandro/open-build-service:wip/adalessandro/aptly-snapshot-prefixdistro into collabora/staging
Task https://phabricator.apertis.org/T8672
aptly: Change snapshot distro/prefix to match reprepro
Reprepro was setting the snapshot Codename (a.k.a. Suite) to
snapshots/distro/timestamp. Let's use the same convention for
compatability.