Fix Cassandra fabric setting seeds
Reduce excessive cassandra-seed logging

- CassandraNode was repeatedly publishing serviceUp, causing log.debug
  every second
- Don't log on fabric stopping (otherwise complains no seeds, with
  scary threat of split-brain)
Merge pull request #1176 from aledsage/fix/CassandraFabric-setting-seeds

Fix setting seeds in CassandraFabric