Fix repository overwrite

Including `/etc/jenkins/debian_glue` in `generate-reprepro-codename` overwrite previously defined `REPOSITORY` variable value.

When using a custom `REPOSITORY` value in `/etc/jenkins/debian_glue`, release packages will be pushed in the wrong repository because scripts also use `REPOSITORY` variable.

This fix renames `REPOSITORY` into `DEFAULT_REPOSITORY` in `/etc/jenkins/debian_glue` and use it instead of hardcoded `/srv/repository` as default value in all scripts.