Partitioning scheme for cassandra hosts

Cassandra hosts have 2 spinning disks and 2 SSDs. Partman should be
instructed to create a /boot partition on the spinning disks. The rest
should be RAID1 LVM root and swap
The SSDs will be manually partitioned after installation

Change-Id: I2c165028c617a2e875fd25291d49512ebba3a95b
Merge "Partitioning scheme for cassandra hosts" into production