Should check exit status of curl commands

We noticed a pretty cool CI failure today:

$ /app/cbuild --debug build-container alpine $FDO_DISTRIBUTION_VERSION $FDO_DISTRIBUTION_TAG
/app/cbuild: line 1: Internal: command not found

The CI template is trying to execute what's probably "Internal server error" as a shell script. Problem must be here where the template does not check the exit status of the curl commands. (Note this is copied across all the various distro templates.) Of course it's doomed to fail if you can't download the script, but it should be possible to fail with a much less confusing error message.