[cassandra] One cassandra per data disk

• One cassandra instance per data disk per server

• One disk per zfs pool

• SSD shared between the cassandra instances

• All the cassandra instances of a server must be consider in the same rack to avoid to have all the replicas in the same server

• 5 nodes at the beginning of the tests

• add the last node during the test

Additional test scenarios:

• Loss of a cassandra instance in a server
• Loss of several instances in different servers
• Loss of a complete server

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Migrated from T4375 (view on Phabricator)