update setup-ring.sh
update setup-ring.sh

- fix license header
- add kill random node
- session-key parameter is mandatory
- SCALARIS_UNITTEST_ variables can be overridden
- fix usage

scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris,scalaris-team/scalaris