create-iso-jenkins.sh: Change output dir name to "nobackup"

We have in our lab a backup system which was getting full with tons of isos
generated by the create-iso program. This backup system would not backup
files inside a directory called "nobackup", and that is why we are changing
the output directory name to "nobackup".

Signed-off-by: Diego Pasqualin <dpasqualin@c3sl.ufpr.br>