Bug on replacing mode git repo url

[zhiyuli]

There is a bug or edge case that would happen when replacing the git repo URL in DB for an existing registered model.
Compute Server git clones model repo from the URL that is recorded in DB. If the URL is changed, Computer will not git clone from the new repo URL. Instead, it continues to use the previously git-cloned old repo because the repo folder with the same name already exists.

This affects

1. rest endpoint /git which would list mixed old and new info: model repo URL is new (from updated DB), but job manifest info is old (read from git-cloned old repo)
2. the "executable" folder on HPC: the contents are copied/SCP'd from Compute server, so in this case it continues to use the old repo.