Ensure clustering works with all Oracle RAC configs

There have been reports of Nuxeo clustering not working well with Oracle RAC. Symptoms are nodes not seeing modifications done by other nodes (bad invalidations propagation).

This happens in situations where different Nuxeo cluster nodes point to different RAC instances. In that case the initial node registration cleanup, which uses V$SESSION.SID, will fail to account for sessions available or other RAC instances. GV$SESSION.SID should be used instead.