Feature/min seed nodes + making things working after upgrade to latest cassandra and mesos

There were so many problems after upgrade that require testing on cluster that it took more than expected.
First there was updates to cassandra-env.sh and cassandra.yml needed. 
Second compilation and deprecation was fixed.
Third needed to use slf4j and set through command line (cassandra-mesos) settings for Jetty to log on INFO level, otherwise it went to DEBUG. 
Forth introduced min no of seed nodes to avoid cluster setup stuck in the middle when offers being rejected due to not started ConfigServer
Fifth changed the name of task so it would be consistent with marathon tasks.