Measure performance of LILAC's redistribution at various processor counts

We should measure the performance of LILAC's data redistribution (between the atmosphere and land decompositions) at various processor counts. We should determine the time it takes both to do this redistribution, and (if possible) determine the slowdown caused by introducing this global synchronization point.

(@gutmann raised this point yesterday; it is something we've talked about doing ever since the initial LILAC proposal, but I wanted to open an issue to make sure it gets done.)

It will probably be easier to do this after #894 is resolved: Blocked by #894 .