Swap follow up improvements part2

[bobbyiliev]

TODO: still need to test this end-to-end

Same as MaterializeInc/terraform-aws-materialize#90

Part 2 of follow ups after enabling swap.

Breaking changes:

• The system node group is renamed and significantly modified, forcing a recreation.
• Both node groups are now standardized with consistent configurations.
• OpenEBS is removed, and with it all support for lgalloc, our legacy spill to disk mechanism.