Right now when using the CI mirrors, one can either:
Use the latest snapshots from all mirrors as mock_runner and all the jobs do.
Use a specific snapshot by using the direct URL to it as we do on slaves.
It is desirable to be able to mark or tag specific mirror snapshots for various uses. The primary use for this is to track which mirror snapshots have been tested successfully by the change queue in a similar fashion to the way we track passing packages by storing them in the 'tested' repo. The motivation behind doing this is described in