Current behavior: both index-repository and index-all-repositories do a git clone --bare $first_remote_url $elixir_root/$project/repo. That fails if the folder exists.

Ideal procedure:

• git init, gracefully failing if folder already exists.
• Add Git remote for all remotes that are not already in the repo. This will add all remotes if the above git init didn't fail.
• Maybe fail/warn if some other Git remotes are present which weren't passed as argument?
• Do a single git fetch --tags --jobs=... remote1 remote2 ... call. We benefit from parallelism.

That will work well once update.py is fixed to not have its indexing depend on the order of parsed tags.