Image Discovery: Need method to discover available version tags

[peebs]

I think it would be desirable to have the ability to discover the available version tags of an appc image name. If there is a discoverable (and signed) manifest that lists the versions and respective hashes it allows a fairly wide variety of client update strategies and remains a static asset that can be updated when someone pushes a new aci.

In my use case, I am running an kubelet aci, I know the maximum safe version to run and I want to discover the latest available aci that is <= to the maximum based on semver tags. I could imagine people also tracking tags like stable and latest and wanting to know when the hash changes.

I believe #415 is related and possibly #211 as well.

[alban]

ping?