swim dissemination not covering entire group
We should base the piggyback transmission count (and protocol period length) off of the group size as in the SWIM paper. The default value was hard-coded to 5 which would only work for really small groups (10s of processes). Even so, some processes aren't getting membership updates, so there could be a bug in the SWIM dissemination. We should validate this.
In the meantime, piggyback tx count has been set much higher (50) to help ensure update propagation.