Realm: Fix Deppart Op Load Balancing Heuristic

[lightsighter]

Realm's load balancing of deppart ops sometimes does the wrong thing, especially in cases where all the sparsity maps for index spaces are local to a node. It's better in some cases to just do the index space operation locally.

[streichler]

@lightsighter Do you have any cases that demonstrate this problem, ideally with an estimate of the magnitude of the potential speedup?

[lightsighter]

I remember seeing it, but I don't remember which application it was. I think it was Pennant. I'm going to be re-benchmarking Pennant pretty soon to measure tracing with control replication so when I do that I will also check if I see slow start-ups when generating the mesh with dependent partitioning.