Works like "ostree refs" but fetches refs from a remote repo.
This depends on the remote repo having a summary file, but any repo
being served over HTTP *ought* to have one.
For Fedora and potentially other distributions which use globally
distributed mirrors, metalink is a popular solution to redirect
clients to a dynamic set of mirrors.
In order to make metalink work though, it needs *one* file which can
be checksummed. (Well, potentially we could explode all refs into the
metalink.xml, but that would be a lot more invasive, and a bit weird
as we'd end up checksumming the checksum file).
This commit adds a new command:
$ ostree summary -u
To regenerate the summary file. Can only be run by one process at a
time.
After that's done, the metalink can be generated based on it, and the
client fetch code will parse and load it.
https://bugzilla.gnome.org/show_bug.cgi?id=729585