redistributeData does nothing for partitions that are evenly spread across dbroots

If you have data loaded near perfectly with one dbroot overloaded but the partitions are distributed across all dbroots, then redistributeData will do nothing. In this case the cluster got into this state due to bug MCOL-786, but it should be possible to also reproduce this other ways such as using mode 1 to load a bunch of rows perfectly and then use mode 3 or limit the load to 1 pm such that that pm has a bunch more data.

This configuration will not do any redistribute, but it should try to reduce the size of the overloaded dbroot and spread this out across the remaining dbroots.