iop: feeds_update: return 1 on failure and add -i to update index only
Handle failures correctly so that CI for example will terminate. Add -i option to update index only and not heads.
Take two of this which allows silent failures when updating the feeds. This is not good but it is necessary as a workaround for the issue with private feeds. This should be solved in a different way. Reproducibility of builds in case of network outages for example cannot be guaranteed as long as silent failure is allowed.