during build. Defaults to /tmp/grml2iso.tmp if unset.
Examples:
- $0 -s http://192.168.23.42:8000/grml/ -o small.iso grml64_2010.12.iso
+ $0 -s http://192.168.23.42:8000/grml/ -o small.iso grml64-small_2018.12.iso
Will generate a file small.iso which tries to download the squashfs file from
http://192.168.23.42:8000/grml/ - the squashfs file is placed in the same