This change helps ensure that nodes for each partition are spread
over all datacenters, a property that wasn't ensured previously
when going from a 2 DC deployment to a 3 DC deployment
- change the terminology: the network configuration becomes the role
table, the configuration of a nodes becomes a node's role
- the modification of the role table takes place in two steps: first,
changes are staged in a CRDT data structure. Then, once the user is
happy with the changes, they can commit them all at once (or revert
them).
- update documentation
- fix tests
- implement smarter partition assignation algorithm
This patch breaks the format of the network configuration: when
migrating, the cluster will be in a state where no roles are assigned.
All roles must be re-assigned and commited at once. This migration
should not pose an issue.
