Fallback to pypi index when wheels not found

PIP attempts to verify all configured indexes for wheels. Thus, setting –find-links or –index-url to only repo_server does create chicken-egg error - it either fails with wheel not found, when it’s not yet built, or always trying to reach remote index, when all is present.

Thus, we set the repo_server as the only index, where it rewrites to pypi when wheel does not exist locally.